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need help with a 12 v to 6 v reducer

5K views 32 replies 3 participants last post by  docvette 
#1 ·
Trying to use the original temp gauge in my 41 pontiac,obviously 6 v. system but converted to 12v. bought a reducer and installed it, worked good on the bench, pegged out once it was installed. After much confustion I checked the output on the reducer, it was a full 12 v. Now I'm told, the reducer has to match the use. The one I bought said 1.5 ohms, 4 amps. counter guy said that was Max. 2nd guy says no, that's exact. If you want to run a 1 amp thing, you need to wire 4 of them in series?????? So the questions are : how do I determine the ohm resistance and amp draw of my gauge? Where do I find one the right size (they carried only the one 4 amp job)? And most puzzling to me, what am I missing? If the reducer cuts the voltage to 6 volts, and the gauge draws less than 4 amps, why does that burn it up? More I can understand, but less?
can someone explain the theory/science behind this? have any other solutions? At $12 each I don't want to run 4 of them, plus I don't know where I would put 4 of them.
 
#2 ·
Doc here, :pimp:

First off, If you have a gauge drawing 4 amps or above...toss it it's way past shot..more like a few mil-amps would be more like it..

Without a LOAD on a resistor..It will show the same voltage in as it does out..Because it is doing no useful work. It is just a straight wire..Current is used in the resistor and changed to heat when a load (the gauge, a light, ect..) is imposed on the resistor..current goes high..voltage goes low. Tell your Guy..whoever told you you need 4 of them..he needs to study OHMS law..sounds like at 12 bucks a pop..he's studied financial management real well...

I=E/R..or

Current = 12 volts divided by 1.5 ohms = 8 amps

To determine the resistance of your gauge, get out your DVOM, set it for OHMS scale, R X 1 or autorange, calibrated for 000, disconnect ALL the gauge wires..measure across the power and ground of the gauge..Whatever that reading may be..say 90 ohms..apply a little more ohms law..

I=E/R

Current=6 Volts divided by 90 ohms = 0.666 amps..(about 1/2 an amp)

You say something is burning up ? what is burning up?


Sounds to me like you don't have a drop problem at all..but a sender wire open or shorted to ground Or a bad sender, Or a mis matched sender.

The easiest thing to do (and a heck of a lot cheaper..)get a 6 volt lantern battery, remove power and ground from the gauge, and jump in the lantern battery..If the gauge pegs one way or the other..the sender wire is open or short, Or the sender is wrong for the gauge. Troubleshoot that first , then go back to a dropping resistor from the 12 volt system.

You may have another remote problem..If the car was 6 volt positive ground, and you didn't rewire the gauge..your putting the resistor between the gauge and ground making the gauge a dropping resistor for the resisror..(it's dumping the load on the gauge) ..

You need to strip those wires and rewire it for negative ground with he resistor feeding the + side of the gauge.be sure the - goes to the body (not power) and the + side goes to the resistor.

Doc :pimp:
 
#3 · (Edited by Moderator)
12v to 6 volt

Thanks for the reply Doc. I'm not sure I understand, but at least you do.

Got the strong feeling the parts guys were winging it. Let me see if I can get this straight.

1. No, I don't have a gauge drawing 4 amps, that was the rating on the voltage reducer, I guess if I did, the parts guy would be happy. .

2. "burned up" was my way of saying, it doesn't do what I think it should do. ( I get so frustrated with electrical issues my common sense dissapears. There was no visibile or olfacotry issue with the reducer at all, it just wasn't "reducing" the voltage.)

3. No reverse polarity problems. It's a Pontiac, negative ground.

4. The lead from the gauge to the sender is a separate, direct wire. I can replace it, but seriously doubt it is broken or grounded, as I looked for that. Which leaves the simplest, most likely, problem. wrong sender.

I'm searching for an original sender, in the meatime I used a generic. Before installing, I hooked it up with the lead and a ground. Took a reading in the open air, about 100 degrees (nice south texas day),
then I held it in a cup of near boiling water, about 200 degrees.

For grins I stuck an ice cube on it and it pegged down. So I figured I was close. Installed it and it went straight to the peg on the hot side.

So, I guess either the sender or the gauge must have had some poor ground until they were properly installed? So, I proceeded, assuming the sender was OK.

How would you go about identifying the proper sending unit?

[If i understand correctly - it is the sender that now has too much resistance, so that must have been the poor ground in my test??

Is that correct? ]

Is there a way to "balance" the sender and gauge, or do I just have to have an original sender? Sorry to be so long winded, but I would rather understand the problem, than just throw parts at it till it works.

don
 
#4 ·
Doc here, :pimp:

OK I edited your post for ease of read..hope you don't mind.. :sweat:

OK, let's address each issue as listed then deal with what remains..
  • OK, sounds like you have the rating for the output side of the drop..If you note it s exactly half of the 12 volt math..

    I=E/R..or

    Current = 12 volts divided by 1.5 ohms = 8 amps


  • The reason it didn't reduce voltage (I assume) Is because there was no load on the resistor.. If you put 12 volts on a 1.5 ohm resistor, and measure to ground , It will read 12 volts..If you then add a 6 volt lamp..It will read 6 volts..at the resistor between It and the lamp to ground.

    If you "Unload" a lamp, by removing the GROUND wire to it..then put a meter between the lamp ground, AND actually GROUND , the lamp will not light BUT it would appear the GROUND wire is 12 volt positive..Yet if you GROUND the junction of meter and ground, it will go to 0 volts and the lamp will light without a "Shorting" Effect..This is because the lamp filament is consuming the current..doing useful work (lighting the lamp) ..


  • Not a Pontiac Guy at all..but wanted to be sure a vehicle of that vintage wasn't "Born" as a positive ground..


  • The sender wire SHOULD be separate..To test for open / Short condition..Get your DVOM, Set it for OHMS , R X 1 , Calibrated 000, run a LONG jumper from the disconnected sender end to one probe on your meter..Remove the wire from the back of your meter..hook your other probe to that wire..The reading should be 000, If not replace the wire..THEN if good, measure that wire (either end) to ground...It should read infinite..If not, replace the wire..If so It's good..

Senders, Are Gauge/Circuit Specific..and Visa~Versa..you Can't just toss a sender at the gauge and expect it to operate accurately...If at all..You need to determine the resistance of the sender circuit on the gauge (On yours, that vintage, I'm guessing 0 to 30 ohms..) And MATCH the sender to the gauge resistance..

A temperature Sender can not read "AIR" It must be immersed in the flow of the media in which it is being tested..(I.E. in the water or stream)

To accurately test, you must boil a pot of water, (212 degrees) and place the sender fully wired AND a lab or other accurate thermometer in the water..

As the water Temps decline , Note the readings on both..If you have a portable hot plate..you can heat it back up, then note the differences as it rises..

Make a list as you do, and you will find the accuracy and linearity of the gauge..and know at a certain temp, it's 5 degrees off for example..

The sender IS probably OK, Just wrong value for the system to be accurate..

To test for Value, Go to radio shack, get a collection of 1 watt resistors..in the following values..30 ohms, 60 ohms, 90 ohms, 120 ohms, 150 ohms, 180 ohms, 210 ohms, and 240 ohms..

Next , monitoring your gauge, place one resistor in line on the sender wire, to a known good hard ground..as the meter climbs , note the value..keep "Upgrading" the resistors until "It Just Barely Pegs" the gauge..note that value..it is the resistance Value you need to get for your sender..

Say that value is 30 ohms..then remove YOUR sender and go to the parts house, and get a value sender that will be 0 to 30 ohms..AND have the same thread pattern as yours AND the same depth..and that will fix that.

BE ADVISED..Some senders work in reverse..It may be that it needs a 30 to 0 to be right..The test still applies, except for the meter drive will be backward, AND when you go to get a sender..be sure it's 30 to 0 not 0 to 30..

If your sender has Less resistance than is required , you can add a resistor on the sender line to bring it within spec, (I.E. a 0 to 30 sender needs to be a 0 to 60 sender..add a 1 watt, 30 ohm resistor) The reverse will apply if the sender is too high, but you need to do a little Math to figure the value, and make that value resistor, go between the sender line and Ground..

The best thing is GET the RIGHT sender..ton's of them in different values out there..

Doc :pimp:
 
#5 · (Edited by Moderator)
12 v to 6 v reducer.

Doc. I need to chew on this a little, but i think I get it.


1. Didn't expect the sender to work right, but thought it would move in some relationship to reality until I could get the right sender. (the parts guy said all senders work in a "similar range", which I now see is bogus)


Yes, I rechecked the function of the voltage reducer, and when I read it after it passes thru the gauge, it is about 9 volts. Do I need to do something to get this down to 6? I also tested the one that supplies the gas gauge, it also reads about 9 volts. If I wire the 2 in series, would that work?


2. not sure I can run the first test, because it just pegs at all temps. Or maybe you didn't intend for me to do that test until I had a gauge that worked.


3. the test for value. OK there, except for the "reverse" part, (if the sender has less resistance than is required) . the gauge only has 2 wires. the hot lead and the sender. I think you are saying to put the resistors between the gauge and its ground, which I can't do easily, cause it grounds to the dash. But we can cross that bridge if we come to it.


4. As a starting point - with the 0 meter set at 20k the sender appears to have a resistance of .15 the gauge had a resistance of .06 Neither hooked up to anything, just a "unit" test. Maybe this is irrelevent.

It just seems that if the gauge pegs when connected [it starts out on the low side and steadily moves to the high temp side to totally pegged within about 10 seconds] would'nt that indicate the sender has less resistance than the gauge ?

Which is opposite those "unit test" numbers. Or I'm thinking *** backwards. Likewise, if I ground the sending unit wire, it pegs the needle. that is 0 resistance right?

So more resistance in the sender line seems to be the answer, except for that "unit" test. So tell me that was a BS test and to ignore that, and I think I have my mind right.


5. The big question. Assuming I can figure all this out, how do i find the right sender? I can only imagine the look I'm going to get when i walk in and ask for a sending unit from 30 to 60 ohms? The usual response is "what make and model car is that for?"


Doc, I sure appreciate this help. Getting the original gauges to work properly just seems like the right thing to do. don
 
#6 ·
12v to 6 v

Doc, I just read my post, and it seems confusing. I used the term sender once, meaning the gauge, not the sending unit in the engine. Might have been confused in your answer also. Your last sentence said "the reverse will apply if the sender is Too high... and make that value resistor, go between the sender line and Ground" ... I read that as gauge and ground. don
 
#7 ·
Doc here, :pimp:

OK once again..with feeling... :D

1. Didn't expect the sender to work right, but thought it would move in some relationship to reality until I could get the right sender. (the parts guy said all senders work in a "similar range", which I now see is bogus)
For your parts guy to say this , is like an electric an saying your 220 Volt Compressor is in the same "Range" as your 110 Volt outlet..Or a 6 volt lamp will be fine in a 12 volt circuit..The only similarity is they are both capable of power and one is double the other..dude needs to study basic electrical before giving that kind of advice..

As little as 30 ohm mis~match is a world of difference to a sender circuit..and he should know that..

Yes, I rechecked the function of the voltage reducer, and when I read it after it passes thru the gauge, (** :confused: as measured on ground?? Thats wrong..you can't accuratly series measure it! :confused: **) it is about 9 volts. Do I need to do something to get this down to 6?

I also tested the one that supplies the gas gauge, it also reads about 9 volts. If I wire the 2 in series, would that work?
Test your meter on the battery, It should read 12 volts or close about..11.6 to 13.95..Be sure your readings fall within spec..If not REPLACE the battery's..It is in error..or use a better meter..

NEXT scrap the second resistor..Tie ALL your gauge power to the one resistor..not two..you only need one..and it may be the cause of a 3 volt rise (cross feeding)


Your readings will only apply, with the full gauge hooked up, ground the sender wire, and measure the junction of the resistor and the gauge..It will read 6 volts IF your meter isn't in error.


3. the test for value. OK there, except for the "reverse" part, (if the sender has less resistance than is required) . the gauge only has 2 wires. the hot lead and the sender.

I think you are saying to put the resistors between the gauge and its ground, which I can't do easily, cause it grounds to the dash. But we can cross that bridge if we come to it.
No, the resistor is installed between the Power and the gauge in order to work..like this:

12 volt POWER------>RESISTOR----->6 volts<---->GAUGE---->SENDER....

4. As a starting point - with the 0 meter set at 20k the sender appears to have a resistance of .15 the gauge had a resistance of .06 Neither hooked up to anything, just a "unit" test. Maybe this is irrelevent.
Set your meter for Ohms..R X 1 Scale..measure between the terminal and the sender body..do this while testing in a pail of boiling water..look at the highest reading..It should be around (example)30 ohms at 220 degrees..then cool it off, read it again..It should be around 0 ohms..(This is Example only..could be higher) This is your "SENDER RANGE" 0 to 30..ohms. It can also be reversed..30 (at high temp, 0 at low)


It just seems that if the gauge pegs when connected [it starts out on the low side and steadily moves to the high temp side to totally pegged within about *--->10 seconds<---*] would'nt that indicate the sender has less resistance than the gauge ?
This would be indicative of a "Close Value " sender..not a proper value one..like a 0 to 60 where a 0 to 30 should be.. If you ground the sender wire, you will see the gauge will peg right now..this is because there is NO resistance in the line..(no sender and hard ground)..



5. The big question. Assuming I can figure all this out, how do i find the right sender? I can only imagine the look I'm going to get when i walk in and ask for a sending unit from 30 to 60 ohms? The usual response is "what make and model car is that for?"

docvette
To test for Value, Go to radio shack, get a collection of 1 watt resistors..in the following values..30 ohms, 60 ohms, 90 ohms, 120 ohms, 150 ohms, 180 ohms, 210 ohms, and 240 ohms..

Next , monitoring your gauge, place one resistor in line on the sender wire, to a known good hard ground..as the meter climbs , note the value..keep "Upgrading" the resistors until "It Just Barely Pegs" the gauge..note that value..it is the resistance Value you need to get for your sender..
That should get you straight..

as far as getting a sender..if they are auto zombie idiots..(sir, I need a model and year) just say it's a S/W gauge on a riding lawn mower..no year no modle it's just an SW 0 to 30 (or what ever you find it is..)

Doc :pimp:
 
#8 ·
12v to 6 v temp sending unit

OK Doc. i think I got it.
When the sending unit lead is grounded ( 0 resistance) it pegs the needle. Takes 30 ohms to get it to read about 220 degrees - as high as it goes.
More resistance, lower temp. 47 ohms - 170 degrees / 68 ohms - 130 degrees and at 100 ohms about 100 degrees, as low as it goes. I noticed it is not a smooth curve. 15 ohms on one end of the scale is about 50 degrees, but 30 ohms difference on the other end is only about 30 degrees. is that normal? big question is - do I ask for a 100 to 30 sender (cold to hot) or the opposite? Turns out the local hot rod shop has many senders, by value, so I'm headed there tomorrow. Thanks, don
 
#9 ·
Doc here, :pimp:

100 to 30 should be fine..If they don't have that you could go 100 to 0 , just remember it"s high on the "Hot" side a little bit..In fact I'd get a couple around that value if they are cheap enough..you can "Fine tune It " a little bit..

When you get it, boil a pan of water 212 Degrees, and hook the sender up , you need to jump the ground to complete the circuit..get an accurate lab or Kitchen thermometer, and submerse them carefully in the water..

Get a Note pad , and note any variances throughout the range as the temperature declnes..(so you know , for instance the gauge is 6 high through , say , 150 to 165..) and keep the list for future referance..If you have a hot plate..that you can bring to the car..you can do it in both directions.

This will give you an accurate idea of your "Linearity" of the gauge.

Doc :pimp:
 
#10 ·
need help 6v to 12 volt

Well Doc, here's an update. Turns out the Hot Rod shop did not have senders listed by resistance. (they seem to know less about this than I do, now). So back to the parts store to browse the Standard catalog. found one that was listed as 24.7 ohms at 220 degrees and 152 ohms at 100 degrees (I figured I needed 33 at 220 and 105 at 100 degrees, but this was as close as I could get). Went home to try the "heating water Test". The gauge pegged before the water got to 100 degrees. (It would start out slowly and about halfway up the gauge just swing over to the peg, as the water got hotter it pegged faster). Almost seems like i have a ground at the gauge or in the wire (I've checked this several times) but when i disconnect the ground from the sender, the gauge doesn't move,(seems if I had a short to ground it would read all the time) Also the resistors placed in the ground wire did make the gauge work properly. Does this make any sense to you? Can you guess what I am doing wrong? Also, I appear to have another problem. My battery went dead after sitting for 4 days (second time), so I put the voltmeter between the negative terminal and the negative cable, I read 10.2 volts. (I expected 0) I get the same reading if I put it between the positive post and positive cable. From reading other posts, I disconnected the alternator completely, but got the same reading. Next I will start pulling fuses to try and isolate this problem. Could this problem be affecting my sender testing?
Lastly, do you have a simple schematic for a mid 80's gm wiring harness with the 3 wire alternator and built in regulator? This one is wired with both leads from the alternator connected together and then runs everywhere. that doesn't seem right to me, and I can't seem to isolate anything cause it just feeds in a circle. Sorry to be so long winded, but most of my hair is on the shop floor. Don
 
#11 ·
need help 12 v to 6 v

follow up to the above. I have now pulled the starter lead, the horn lead, all the fuses and flashers. my 10.2 volts is now around 9. Is it possible to have a short in the battery itself, even though it tests at 12v from terminal to terminal and it was OK'd at Auto Zombie?
Footnote - I have new ground straps from the engine to the frame, frame to the body and body to the engine and all ohms tests from dash grounds/headlight grounds/etc. all read no resistance.
 
#12 ·
Doc here, :pimp:

Whoa...STOP!!!

YOU can not take a useful reading on VOLTS DC In SERIES with the load...(as outline two posts back) The only thing you will see is buss voltage and the fact that somewhere in the system , there exists a proper ground through a device..

If you place a DC VOLT meter between the ground on the lamp and hard ground..then turn the lamp on..your meter will read 12 volts, but the lamp won't light..Leave it on for a month..will the battery go dead? ..No..No load..or useful work is implied on the battery..(lamp is not lit EVEN though it says 12 volts in series..)

DC VOLTAGE READINGS are always taken in PARALLEL , Or across the LOAD..or the battery..+ and -..To check your state of charge..put the meter ACROSS the battery, engine at rest..it should read around 12 volts if it is charged..much below , could indicate a bad cell..

NOW, Start the car..let it warm and the high current surface discharge about 5 minutes to recover..then measure AGAIN, ACROSS the battery..It should read between 13.95 and 14.4 VOLTS DC...If the alternator has an output.

NEXT, to measure AMPS..ALL READINGS are taken in SERIES with the circuit..To Do that, remove all load sources..(Domes, hood lamps trunk lamps, anything that will draw power while you test) Remove the battery cable from the battery, CONFIGURE your DVOM for AMPS, and set it for the HIGHEST scale, (usually 10 amps).

Place one Probe on the battery terminal, the other on the Battery CABLE, note your reading as you do..If it pegs you have a major problem that your meter will not be able to handle..stop immediately , or you'll destroy the meter..get a higher AMP Capable meter..or seek help from a local auto electrical shop..If it reads low on the scale..reduce the scale until it "Just" tops out..That will be your actual reading..

On a modern vehicle with Computer, CD player with memory presets, Alarm systems, and the like, it should read between 0.3 and 0.8 (less than 1 AMP) to be good..any higher..you have a problem.

If that's the case..The first logical step , because it is the most common offender, Is disconnect the Alternator complete from the system, and recheck the AMPS reading in SERIES with the battery..If it falls back into Spec, replace the Alternator, OR you can get a diode/Regulator and rebuild kit, for around $15..and an hour or so of your time..



If no change, on the readings, If your Fuse buss is Well marked, pull ALL the fuses and relays from it and recheck the AMP draw again..If it is within spec, or lower, one of the branch circuits are the culprit..

While you have them out check ALL your fuses for CONTINUITY across the fuse, (it is not your cause of the problem, but you'd be surprised how many are found bad..and how much "stuff" begins working after) ..replace any bad ones..Don't eyeball them, the filament can open at or near an end or "blade foot" and you'll never spot it..use a test lamp or DVOM set for Continuity, or Ohms R X 1, calibrated 000.

Replace the fuses back in the buss one by one, watching your Current draw in AMPS..when it jumps up (above an amp) that is your offender..Troubleshoot that branch circuit. Repair or disable as needed. Continue until all are back in the fuse buss.

The Sender you have (numbers wise) should be the right one..Try your test again with just the sender hooked up to your meter, set it for OHMS , R X 1 Scale, Calibrated to 000, hook one probe to the center terminal and the other to the sender body, and carefully retest your sender..with / against your lab thermo..note the ohm readings as it ascends / declines and be sure it is the sender advertised on the box (they mix them up some times..) If it is..then I'm thinking you have a gauge linearity problem.. If the sender test "True" post back, I can give you a circuit you can build that you add in line to "Gain " linearity over the range..

Also, there may be a problem with draw through the dropping resistor to the gauge, try putting an instrument lamp on the power side of the gauge..this will keep the draw constant through the resistor as the gauge resistance to ground is changing..If that works, you'll need to wire the lamp up to the gauge + and ground , permanently, or install a 6 volt instrument regulator ..

The Alternator sounds like it's wired correct. The main output from it to the battery via Fuse link or maxi fuse, the red terminal jumpered to it, and the brown wire to the Idiot lamp, bypass resistor and fuse into the switch.



Doc :pimp:
 
#13 · (Edited by Moderator)
6v to 12 v help

OK Doc. Can't say I really understand, but I believe you.

Tonight we did the following. Put a meter between the positive battery post and the positive cable, set to amps. There was no draw at all.

opened the door, the dome light pulled about .6 amps. with the door open and the ignition on we pulled about 1.2 amps.

plugged all the fuses, etc. back in, hooked up the alternator, hooked up the starter, no changes.

With the key off and door closed, we had no draw at all on the battery.

Drove to Auto zombie. they checked the battery at 12.75 volts. did a draw down test, it never got below 11.75 and bouced back to 12.75 when the load came off. With it running the alternator was putting out just over 14 volts, and the battery was taking a charge. There appears to be nothing wrong with the system at all. Guess we'll wait another 3 or 4 days and see if the battery is dead again.


Now for the temp gauge. We repeated the ohms resistance test.

30 ohms resistance the gauge reads about 220 degrees,

at 100 ohms resistance, it reads about 100 degrees.

Same as before. Tested the sending unit with an ohm meter. Cold it was at 170 ohms,

as the water warmed it up the resistance dropped.

at boiling it read about 30 ohms resistance.

Independently they both work and seem to have fairly relative values.

In the car, hooked up, with the temp sender end submerged in cold water, the gauge will climb slowly until it pegs.

As before, if we heat the water, it just pegs faster.

You referenced something I didn't fully understand, but I think
you were reffering to the voltage reducer.

So we put a test light from the power side of the gauge to ground, it lit up, but was pretty weak as it was a12 v light.

As we ran our sending unit tests again we at least got some reading (like 180 degrees on the gauge while the sender was in cold water) but it didn't peg, so I think we are on to something.

you mentioned a 6v instrument regulator. Can you explain?

Also, It may not be relevent, but the gas gauge is hooked up to the same voltage reducer as the temp gauge, and it works fine?
 
#14 ·
Doc here, :pimp:

OK, I edited your post to make it bit easier to follow..hope that's OK by you.. :sweat:

First, It sounds like your charging and electrical system is functioning fine..and the battery is up to snuff..It may have been a fluke before , something sticking on..running the battery dead..as you said, watch it for a few days and see where it goes..

Something to check, the belt may be "Just" loose enough not to charge under Peak loads .. recheck that and tighten a bit if you think it needs it.

Now about the Instruments, You may not have enough of a load on the dropping resistor to effect enough of a voltage change on the instruments..

A regulator does not depend on the output load to drop voltage..it's 12 volts in a chip, and 5 or 6 volts out , regardless of if it has anything hooked to it or not consuming power..

You can get an instrument regulator at any auto parts store for Dodge or Chrysler in the mid 60's to 80's range of years..If you can't find one I can tell you how to build one from a hand full of parts you can get at rat shak..consists of a 3 terminal regulator chip, a heat-sink, some 18 gauge wire and a bit of your time..wire it power into the chip, ground , and 5 volts regulated out..The only rule is you must keep the draw UNDER 1 amp..(instruments won't draw that much..)

Just had another post on here SAME issue..the guy built one , installed it and was simply amazed how well they worked after all these years.. :D

This is one of the "Little headaches " that crop up on "split buss" systems..(Why I do not like splitting a buss..6 and 12..and advocate all or nothing at all..)

Doc :pimp:
 
#15 ·
12v to 6v help

Sounds good to me. Need a break from electrical to work on something I understand. Called my local parts store (the one that actually tries to find things they don't stock) and they found several listings for Instrument Cluster Voltage Regualtors, $50. Do you have a particular preference -make/year/model? Or are they all the same? Unless I can build it for less than half of that, I'm better off buying one.
Assume this would replace the voltage reducer I have, and I would run both temp and gas gauge off of it.
Using the schematic you show above, Where would I hook in my amp gauge?
Seems like it would have to be in one of the two red lines, not where the idiot light is. (FYI. My horn relay is a small aftermaket one that is wired thru a fused circuit, powered only when the switch is on, not part of any original harness, so I can't go there, but I get the idea).
don.
 
#16 ·
Doc here, :pimp:

$50 bucks is a major mark up... :pain: You can buy one if you want to go that route..Or build one for under $20 bucks... :D

You'll need to go to Rat Shack, and get the following, :
  • One 7905 POSITIVE regulator..about $2.95
  • One micro processor heat sink about 3 inches square..($5 to $8 bucks)
  • some heat sink grease, and a 3 tab regulator mylar gasket (under $2.00)
  • a .1 ufd disc cap (2 for 49 cents)
  • a red ring terminal
  • heat shrink tubing for regulator leads

Look on the back of the card the regulator came in, it should read left to right as you look at the front of the regulator, "Input" , "Ground" , "output", ..

You will mount the regulator on your heat-sink material, drill a 4/40 tap hole, and chase the hole with a 4/40 tap..next apply some heat-sink grease, then your mylar gasket, then more grease, then mount the regulator...

Next, solder a red 24 gauge wire to the input side of the regulator, (far left), and leave a pigtail as long as you need to get it to a SWITCHED 12 volt , 1 amp fused source..make this wire RED..

Along with this wire, solder your .1 ufd cap between the ground (center terminal) and this terminal, wrap a few turns of the cap leads to the bottom of the regulator leads and solder, then position the cap and leads so it will "Stand up" parallel to the regulator, make sure the lead on the left terminal does not hit ground.

Next , solder a 24 gauge wire to the center leg of the regulator, , make this wire black, run it as far as you will need to make a good properly bonded ground, burnish paint, grease, dirt, to bare metal, install a star washer and lock , your red ring, and then ground the terminal..

Finally, install a 24 gauge wire to the right terminal, leave enough wire to go to the Gauge power wire,

Lastly, install on each wire, about 2 inch pieces of shrink tube (do this before you hook it up..good thing to tell ya last huh? ) Slide it up the wire to the regulator terminals and shrink them down..be sure that the left and right terminal can not hit the heat sink, or they will short out..If you worry about it, you can install a small piece of electrical tape under the terminals in addition to the tubing..

TO TEST:

Apply 12 volts to your RED wire, And ground to the Black wire Or heatsink..then with your DVOM set for DCV, 12 volt scale, read the orange wire, It should read 5 volts..If you have that, your good to go..install it..

You may note the regulator is running at 5 volts instead of 6..that is because of it's make up, it is a 5 volt regulator..instead of 6..

I say use this one simply because 6 volt regulators are much harder to find at rat shack..and the gauge will never notice the difference..

It is designed to run at + / - 20 % of input voltage..the voltage swing on the old generator system was worse that that under a full load..so you should not have a problem..HOWEVER, ask for a 6 volt regulator first, if you can't get one use the 5 volt regulator..as long as you have 8 volts at the input it will be rock solid 5 volts at the output..(no swings)

The only rule, do not exceed 1 amp on the output..(a gauge system will not exceed this..) But do not "ADD " anything else to it or you'll blow fuses..If you need more, split the loads up between multiple regulators and mount them on the same heat sink.

Doc :pimp:
 
#17 ·
12v tp 6v gauges

You were right about the mark up Doc. I found one for $20.00. VRC601 Instrument cluster voltage regulator. All chrysler products mid 60's to mid 80's. Wired it in, in place of the voltage reducer, both gas gauge and temp gauge. Turned the switch and got correct gas gauge reading and about 100 on the temp with the sender in cold water. In about 5 seconds both of them quit. Like I pulled the power. Checked all the grounds etc. tried again. lasts about 5 seconds. By then the water was hot, and I was back to square one. The temp gauge will read about right for a second or two, then roll over to the peg, just before the whole thing shuts down. Assume the voltage regulator has something in it that is shutting it off?? Possibly responding to the same thing that is pegging my temp gauge?
I'm clutching at straws here Doc. - my temp gauge does not have a separate ground, it grounds thru the case. Maybe I should dis assemble it and be sure the leads aren't grounding internally somehow. Would that explain both of these phenomenon? (ps, for the one second reading I get before the gremlins take over, I think the sender/gauge is matched somewhat)
 
#18 ·
Doc here, :pimp:

I'd Be willing to bet, Somewhere on that 6 volt power line, some ham handed mechanic wired in a 12 volt device...Panel lamp, radio, ect...

The regulator Chip is only good to and amp or two..much over that draw, It will overheat and go into thermal shut down..(off until Cool ...until it finally overheats and goes thermal forever..)

AND that sounds like exactly what you may have...

First Do as you suggested..Carefully pull the covers and be sure you have a good case ground..(It couldn't hurt at all..) and if you feel you need to add a Wired Ground to each instrument..

NEXT Remove the Power wires altogether from the power pick up on the gauges..wire the output of your Instrument regulator to the gauge power Terminals (insure nothing else is on that wire..but the gauges you wire)

NEXT, wire the 12 volt side of your instrument regulator to a known reliable 12 volt switched source.

IF yours requires it, Wire the regulator Ground to a good , proper bonded ground , burnish all paint, grease and dirt down to bare metal, use a star and lock washer.

If that sets it right..you have a 12 volt device on the old 6 volt feed miswired..You will no longer need that circuit , so strip it out all together and you'll probably find a 12 volt item not working..

If I'm correct about what I suspect, this is a very minor malady , of the potential problems running Split busses...

This is why I DO NOT advocate them, and why I always recommend the "All or nothing at all " approach to a single voltage buss..A serious problem could occur, the other way around..a HIGH draw 6 volt item wired into a 12 volt buss..

Check it out and let me know..

Doc :pimp:
 
#19 ·
6v to 12 v help

Well Doc. I did all those tests and came up blank, so I pulled it out and went back to the bench. It is definetly the gauge. Funny it didn't do it the first time I ran the resistance tests, but it is doing it now. Maybe that original voltage reducer didn't reduce enough and messed it up.
fortunately, the car came with a spare in a box of stuff. It's an after market, but pretty close. It has been modified with what looks like some resistors soldered to the field terminals, so of course the values are different, but I can handle that. I'll let you know how I make out in a day or two.

In the meantime, what about the amp gauge? It works, but is not hooked up. I've heard not to use it, and others who have had no trouble. i don't know of an aftermarket volt meter i could substitute into the pod. Got any thoughts on using the original?
If so, Since my system is wired in parallel (I assume that's what it is since my two alternator wires are connected in the middle) can I hook the gauge in one side, or do I have to split them to wire it in in series?
According to AZ, my alternator was putting out 52 amps under the load test. I assume that is the combined output from both sides? Also hope to add A/C soon, so factor that in.
Also, I can find no fusible links in the system. Your diagram shows one on each leg. Should they be closer to the battery, or closer to the alternator? What amp rating would you recommend?
BTW, you mentioned running 2 busses. 12 v and 6 v. Not sure what that means, cause I don't know what a buss is. Everything on the car is 12 v, except the gas and temp gauge.
Doc, is there any way to repay your kindness here?
 
#20 ·
oldguy829 said:
Well Doc. I did all those tests and came up blank, so I pulled it out and went back to the bench. It is definitely the gauge. Funny it didn't do it the first time I ran the resistance tests, but it is doing it now. Maybe that original voltage reducer didn't reduce enough and messed it up.
I'll let you know how I make out in a day or two.
That's pretty rare to find the gauge inaccurate..usually it is operable or not..but good catch..let me know how the new one works out! :thumbup:

In the meantime, what about the amp gauge? It works, but is not hooked up. I've heard not to use it, and others who have had no trouble. i don't know of an aftermarket volt meter i could substitute into the pod. Got any thoughts on using the original?
I Don't like them, never did..they are dangerous in my opinion..When you have full battery potential , that is hot 24 / 7, 365....at the dash board and wires carrying it through the firewall..that you can drop a tool on, or catch your watch band..and burn holes in the metal..and maybe injure yourself..PLUS on most..If the shunt burns out in the gauge..your powerless..

Some will tell you "I've used them for 30 years, Never had a problem.." It only takes one time...to go tragically wrong... :pain:


If so, Since my system is wired in parallel (I assume that's what it is since my two alternator wires are connected in the middle) can I hook the gauge in one side, or do I have to split them to wire it in in series?
I don't understand what you say when you say it is wired two in Parallel? Do you have 2 battery's? Two systems or what? If your referring to 12 volt / 6 volt..you are not feeding both separatly..(at least I would hope not..) If so you are overcharging the 6 volt buss..

The Amp gauge will always install between where the battery bolts to the source (like at the starter, ) and the load, the WHOLE car where the fuse buss wire connects at the starter solenoid....Current will go through the meter on to the car ..to be effective..


According to AZ, my alternator was putting out 52 amps under the load test. I assume that is the combined output from both sides? Also hope to add A/C soon, so factor that in.
There should be "No two sides.." THERE SHOULD BE ONLY ONE OUTPUT from the alternator going to the battery terminal at the solenoid...anything else is something different.


Also, I can find no fusible links in the system. Your diagram shows one on each leg. Should they be closer to the battery, or closer to the alternator? What amp rating would you recommend?
Fuse links were not installed at the factory until after 1970..so it's not surprising you didn't find any..With your current system, a 70 amp link should be fine..your alternator is probab a factory 63 amp unit. The fuse links will always install at the battery end of the circuit or at the solenoid...ALWAYS INSTALL THEM IN THE ENGINE BAY NOT INSIDE THE CAR...

BTW, you mentioned running 2 busses. 12 v and 6 v. Not sure what that means, cause I don't know what a buss is. Everything on the car is 12 v, except the gas and temp gauge.
A buss is a system of wires that joins together at a common fused point..one main power wire in to a brass bar...and several smaller FUSED outputs coming off that bar..a split system is a 6 volt bar and then a 12 volt bar...separate from each other.


Doc, is there any way to repay your kindness here?
Yes there is...do your wiring safely, and then, enjoy your rod when your done!!

Doc :pimp:
 
#21 ·
12v to 6 v temp sending unit

Here we go again Doc. I just don't know enough to ask an intelligent question.
There are 3 wires coming out of the alternator, as in your diagram. (One off a terminal on the top, the other out of a push in connector along with the brown wire). 2 of them look like 10 ga. power wires (Red). They connect in the middle and it looks like one goes to the battery, via the starter, and the other to the main fuse block. (guessing here cause it goes into a large harness). When I say they are connected in the middle, literally, about 2 feet out of the alternator it looks like the insulation was pulled back and the 2 wires are clampled together with a big staple(?), wrapped in electrical tape, and then both continue on) Guess I misunderstood again. I thought one sent power to recharge the battery and the other to the system based on demand. That's why I was puzzled to see them connected together. (also thought this was an example of parallel wiring - which is still a mystery to me).
So. I will install a 70 amp fusible link in the wire coming off the solenoid. Your diagram showed 2, so I wondered where to put the second, since I don't have the typical horn relay.
Reason I ask which side to put it on, based on my assumptions above - I assumed the lead to the fuse box would not carry as much power as the line to the starter/battery, so it might be safer, but I don't know what the hell I'm talking about. . Yes, I can see how a defunct gauge would shut you down.
I've attached a picture of a gauge. Think I might find a volmeter gauge I could sub in for one this size and shape? Don't know when they went to voltmeters, but from about 55 on they seem to favor round gauges, or idiot lights. I could probably swap out the face plate to make it look OK. I really wanted to avoid some aftermarket gauges hanging off the dash.
thanks again, don
 

Attachments

#22 ·
Doc here, :pimp:

OK, to Clean all that up, Strip out that wire..(except the brown wire..)

Install a fuse link at the Starter solenoid..70 amp. From there run One 10 gauge wire to the big bolt on the alternator..

From the top plug, locate the red wire there, and cut it long enough to reach the big terminal, and cut it and install a ring terminal, Bolt it to the big terminal.

The brown wire will remain the same.

You need only 1 fuse link this way on the alternator.

Next on the wire that brings power to the car..to the fuse buss (panel) , locate that wire (should also be on the solenoid, or single terminal at or near the battery..(It's the wire that when you pull it, the whole car goes dead from power..) Install a 70 amp fuse link there. This will protect the whole system..

That "Wire" that you said was crimped..sounds like the fuse link..but scrap it all and do it as above. It's Cleaner.



As far as that gauge..

Try these guys,
Gauge restorations

Tell them you'd like to convert it to a volt gauge and also will need the gauge re~silk screened to match a volt gauge from amp meter..See if it is cost effective, and what they can do for you.

Doc :pimp:
 
#23 ·
12v to 6v help

OK Doc. Before I rip it's guts out, let me walk through it once. Never used this "quote" response, so bear with me.

docvette said:
Doc here, :pimp:

OK, to Clean all that up, Strip out that wire..(except the brown wire..)

Install a fuse link at the Starter solenoid..70 amp. From there run One 10 gauge wire to the big bolt on the alternator..

From the top plug, locate the red wire there, and cut it long enough to reach the big terminal, and cut it and install a ring terminal, Bolt it to the big terminal.

The brown wire will remain the same.

You need only 1 fuse link this way on the alternator.

Starting with Red1 - this wire comes from the big terminal on the alternator and goes to a terminal block on the firewall (along the way it is connected to Red2). Here I unwrapped a lot of black tape and found a fusible link, hand twisted in line no less, and then it goes to the Battery terminal on the starter solenoid. I am to take this out and replace it with a new 10ga wire directly from the alternator to the solenoid, with a new 70 amp fusible link.
Red2 comes out of the alternator at the push in terminal (next to the brown wire) and after connecting with Red1 goes to the buss. I am to cut it off about 6 inches out and jump it over to the same terminal as Red1.


Next on the wire that brings power to the car..to the fuse buss (panel) , locate that wire (should also be on the solenoid, or single terminal at or near the battery..(It's the wire that when you pull it, the whole car goes dead from power..) Install a 70 amp fuse link there. This will protect the whole system..

I'm guessing you are talking about Red2, but the end away from the alternator. It connects to the buss on one end, and via it's connection with Red1, effectively goes to the battery terminal on the solenoid. this link would be missing when I pull Red1. You want this to be a direct link from the Buss to the battery terminal on the solenoid, with another 70 amp fusible link. Note; The positive Battery cable has a secondary lead (looks like 10 ga.) that is not connected. Would it be appropriate to run Red2 to this lead (directly to the positive battery terminal) with the fusible link? Seems like this is its ultimate destination, or does it need to be at the solenoid so it is connected to red1?
If I'm wrong about Red2 being the right wire, I'm lost. There is a heavy wire from the buss to the other terminal on the solenoid, but I thought that was coming from the ignition to the starter. Not a power wire like you describe. The only other large wire from the buss dissapears behind the engine and I think hooks up to the distruibutor for the ignition circuit. Again, power out, not in.

If I understand so far, then the brown wire for the alternator must be a feedback wire that tells it how many amps to put out? Where does it originate?

That "Wire" that you said was crimped..sounds like the fuse link..but scrap it all and do it as above. It's Cleaner.

Hope your next message doesn't start with " whoa - Stop" LOL.

As far as that gauge..

Try these guys,
Gauge restorations

Tell them you'd like to convert it to a volt gauge and also will need the gauge re~silk screened to match a volt gauge from amp meter..See if it is cost effective, and what they can do for you.

I'll give them a try. You apparently don't believe there is a safe way to use an amp gauge.
Doc :pimp:
I'm going to send another reply, RE the temp gauge. I need to keep these issues separate. don
 
#24 ·
12v to 6 v temp sending unit

We are making progress here Doc. Picked up another sending unit that was supposed to match my needed values. Wired it all up on the bench and, damn, it worked. Of course, we now get to talk about "linearity" (sp).
After chasing it up and down the range with my little 2 cup coffe maker and a candy thermometer, I narrowed down the problem. Not sure this is Kosher, but what the hell. I wired a 100 ohm resistor into the sender line and got an accurate reading from about 160 degrees to 180 degrees. At about 195 degrees I had to replace it with a 70 ohm resistor to get the right gauge reading, at 210 I had to drop to a 30 ohm resistor. [the specs on the sender were 450 ohms at cold to 30 ohms at 220, so the sender could be performing properly, just not linear with the gauge, is that right? ]
If you are going to tell me what I think you're going to tell me, speak slowly and use small words like you were talking to a child. skip that, todays kids would probably get it before I do. Just remember, the gauge has been modified once already. don
By the way, I had one of those spiritual moments, Just sitting there looking at a temperature gauge that was working.
 
#25 ·
Doc Here, :pimp:

OK, on the first post..

To make it simple..just strip the red wire from the solenoid that goes to some "mid~point " splice and tons of tape where the second red ties in..

In other words all that should be left on the alternator is THE BROWN wire and a Stub of the red wire from the top plug, next to the brow wire ...

NOW, run a 70 amp fuse link directly from the starter solenoid battery cable bolt, then attach a RED 10 gauge wire to it, route that to the alternator, at the bolt or + OUTPUT lug at the back..and cut the wire...

Next take your second red, The Regulator switching, route that from the plug to the area of the + bolt or lug on the back of the alternator cut that there....Strip both wires, and Get a YELLOW ring terminal, CRIMP BOTH wires into it, and bolt it on the + lug bolt...
Leave the Brown wire alone , it is the idiot lamp..

You need only one fuse link for this circuit as your running an equiv, circuit, through the same link using one wire.

OK, On the Sender..It is perfectly acceptable to "Pad" a range for linearity, SO long as the upper scale of temp is not off the map..
I.E..It does not go from 180 to peg...

and the errors are only a few degrees + / - actual, otherwise you might as well not run a gauge at all..just get a lamp..it would be as accurate.. (maybe) Point is..If it is way out of the ballpark..except for one "small range".. you run the risk of engine damage..

If it gives a Good range that you can live with , and are aware of the errors at certain points..get that value resistor..in a 1 watt version ( or 2 1/2 watts twisted and soldered together) and solder it in line on the sender wire. 1/2 watt will probably get a little warm..

Doc :pimp:
 
#26 ·
6v to 12 v conversion

Hey Doc, got sidetracked with vacations etc. About the linearity on the temp gauge/sender issue. You recommended 1 watt (or 2 half watt) resistors. I noticed radio shack had some 10 watt resistors that looked nice and stout, with apparently a heat resistant shield, that would apear to be more durable under the hood. What is the effect of using 10 watt, rather than 1 watt, resistors in this application? don
 
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