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Old 02-03-2013, 11:29 PM
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voltage problem?

I just got a 1970 Cadillac Hearse for Christmas. The battery was 8 years old, and would run down when trying to start it.
I replaced the battery and at idle it's got around 12.4 volts with no lights on, only radio. It's got 11.8 with the lights. When revved, the voltage goes up to just above 15 volts and the lights will get a lot brighter. Checked at the battery and at the batt terminal on the alt. and at the red wire in the connector for the regulator.

I pulled apart the reg. (external) and it's brand spanking new. I think that the alternator is pretty new too.

I checked all the wiring, and it seems good, no cracks or breaks.

The yellow and blue wires going from the connector on the alt. to the reg. both show near 2.84 both at the alt. and at the reg.

I checked all of the fuses, no blown fuses, and all have good connectivity.

What am I missing?

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Old 02-04-2013, 03:38 AM
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You might need a more better alt....lol

I switched mine from an external reg to a new internal reg alt, very easy to do....... No more dim lights, slow heater motor etc.....
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Old 02-04-2013, 06:35 AM
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Quote:
Originally Posted by Super70DeadSled View Post
I just got a 1970 Cadillac Hearse for Christmas. The battery was 8 years old, and would run down when trying to start it.
I replaced the battery and at idle it's got around 12.4 volts with no lights on, only radio. It's got 11.8 with the lights. When revved, the voltage goes up to just above 15 volts and the lights will get a lot brighter. Checked at the battery and at the batt terminal on the alt. and at the red wire in the connector for the regulator.

I pulled apart the reg. (external) and it's brand spanking new. I think that the alternator is pretty new too.

I checked all the wiring, and it seems good, no cracks or breaks.

The yellow and blue wires going from the connector on the alt. to the reg. both show near 2.84 both at the alt. and at the reg.

I checked all of the fuses, no blown fuses, and all have good connectivity.

What am I missing?
A general rule of thumb is the alternator should turn 3 times the engine rpm (3:1 ratio). You might be able to fit a smaller diameter pulley to speed up the alternator relative to the engine rpm. This will help if bringing the idle speed up a little increases the output of the alternator to about 13 v or more.

Conversely, if there's a way to use a different (larger) pulley from the crankshaft to turn the alternator, that will speed it up as well. Obviously this would mean the alternator brackets would need to be modified.

But at the end of the day, I agree with EOD Guy- replacing it w/an internally regulated alternator is the way to go. At best, the alternator you have is good for ~60 amps. Switching to an SI series alternator can get you more amps at a lower rpm as well as clean up the engine compartment by getting rid of the regulator.
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Old 02-04-2013, 07:34 AM
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clean connections ?

Recheck all the connections. Clean, wire brush- sandpaper what ever is necessary. and check and clean all the grounds. regulator case to mounting is also a ground. too much resistance and the regulator thinks the battery is charged.
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Old 02-04-2013, 07:54 AM
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electrical

EOD Guys right, switch to an internal. However, Cobalt 327 is right also. I'm also curious to know what amp alternator is on there currently? It may be new or newer...but doesn't mean they replaced it with the proper amp alternator. They have a couple different amp alts that would bolt directly in place.
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Old 02-04-2013, 08:43 AM
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Quote:
Originally Posted by timothale View Post
Recheck all the connections. Clean, wire brush- sandpaper what ever is necessary. and check and clean all the grounds. regulator case to mounting is also a ground. too much resistance and the regulator thinks the battery is charged.
^^^^^^^

Do this!

Look, everyone wants to simply slap in a newer alternator, but the fact is, these cars charged just fine when they were new. If the alternator and regulator are new-ish, then you've got corrosion somewhere in the wiring. One place most people overlook is the junction block at the horn relay. I've had exactly this problem due to corrosion there.

The reason a newer alternator fixes the problem is because you replace all the possible corroded connections when you install it.
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Old 02-04-2013, 10:33 AM
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voltage problem

All good advise but let us not forget to check condition and tension of alt. belt
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Old 02-04-2013, 12:30 PM
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Alternator

True that Mr. T...its best to eliminate the simple and obvious things first.
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Old 02-04-2013, 03:54 PM
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The reason I say "slap in a new alt"...... As mentioned above the older alts put out lower amps and if it were ever replaced you might have gotten the lowest amp alt that was ever made for that vehicle etc..... old wiring, corroded connections, hacked wire harness, tapping into already maxed electrical system...... the list goes on and on.

So for less than a hundred bucks for a couple new wires and an internal regulated alt all your low amp problems are solved, heater is hot, the fan blows strong and the lights don't dim as you turn more stuff on etc...... and most important the battery doesn't go flat and leave you stranded.

By far the best thing I ever did for my ride.
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Old 02-05-2013, 09:49 AM
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Quote:
Originally Posted by EOD Guy View Post
So for less than a hundred bucks for a couple new wires and an internal regulated alt all your low amp problems are solved, heater is hot, the fan blows strong and the lights don't dim as you turn more stuff on etc...... and most important the battery doesn't go flat and leave you stranded.

By far the best thing I ever did for my ride.
I'm cheap. For zero bucks cleaning the terminals usually does the same thing...
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Old 02-05-2013, 10:00 AM
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I also agree w/cheap. Ideally, the swap would be made when the original alternator bit the dust. The swap takes basically no additional money, only some time.
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Old 02-05-2013, 12:10 PM
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Test the positive cable , Had the same problem. Replace it and it started better then ever! Also a 8 year old battery is 4 years past due for replacement.
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Old 02-05-2013, 12:50 PM
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If you have these cheap clamp-on terminals, forget about it!



Much better to use a new cable or one w/good terminals:

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Old 02-07-2013, 12:21 AM
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WOW!! I really can't believe that I got so many replies!! I'm still waiting for a reply at another forum!

But, I was thinking about changing out to an internal, just didn't want to change anything. The harness is all original, (I think) and just wanted to keep it that way. I think I'll try cleaning everything first, and if that works, I'll keep it like that for now. But after seeing how easy it is to change over, I think that I'll do that maybe spring time.

I know, I'm in California, and how cold can it really be? That's not the point. I have many cars to work on, and I need to prioritize!

Thanks so much. First thing I'll check the resistance on the battery positive cable again. I checked before, but it wasn't hot. I'll go for a drive and see if that makes a difference. Then I'll clean the terminals.

But looking at the conversion picture, I don't have a junction block, and I don't think that there is a wire from the battery terminal on the alt. to the horn relay. I'll double check though. But could I just jump #2 (white wire) to the batt. terminal on the alt. and just connect the #1 wire to the brown?

Right now there is a wire from the batt. terminal on the alt. to the battery + and the harness for the #1 and #2 white and blue wires to go to the reg. and another red wire in the harness that goes from the batt. terminal to the regulator. Is this correct? Or maybe here lies the problem?

Once again, I'll double check everything. I have Friday off, so I'll play with it then.


Again, really thank you guys.
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Old 02-07-2013, 12:58 AM
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a few things, peoples memory of how things where back then are foggy at best..
yes that ex reg alt at 45 or 68 amps worked in the 70 but they all even when new cars the lights dimmed at idle.. not as bad as with replacement halogen headlights that draw more power than the 1970 tech standard bulb..
also.. the wire'n is 43 years old.. the connections are only one part of the problem.. the wires are also..

I'd change to an internal alt.. a 1985 pontiac t/a (with 305ho) will be a 98amp alt and 30-40 bucks(you will need to change pully to a v belt pully),, I bought a new delco for my 71 truck and it was a whopping 80 bucks..
the rewiring is simple and cost almost nothing..
next, I'd add a relay for the headlights.. it takes the load off the wireharness and headlight switch.. and is a very simple upgrade that cost almost nothing.. every 80-90 mopar k-car based car(all the front drive cars) have a 2 relay bracket on the drivers side struttower.. that gives you a bracket to hold the relays and 2 relays.. few feet of wire and your good to go.. and your headlights will get a full 14.5 volts instead of 11.7 like my 71 truck was getting going through the stock wiring..
if you're really cheap you can get a 98amp internal alt in a junkyard. easy..
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