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electrical confusion

3K views 36 replies 8 participants last post by  ntfday 
#1 ·
Just finished headlamp relay circuit (built self) this is a 2 headlamp system, 76 corvette (has no high beam lights connected to headlamp circuit).


When turned on lights - both headlamps blew. (h4 80/100 watt).


Circuit is:


orig headlamp wires one side only: (high/low) to coils of 2 "bosch" style 5 wire 30amp relays - n/c terminals not used.

grounds all are to chassis: 2/14ga from lights - 2/14ga from relay coils.

power in: from "batt" connection on alternator thru 30 amp fuse. 12ga. approx 2ft long. to both n/o terminals on relays.

power out: to headlamps from n/o on relays: 2/14ga for high / 2/14ga for low.

all connections made with crimp connectors, heat shrink & dilectric grease, except terminal to alternator which is both crimped & soldered.


Never blew headlamps before, replaced for relief to h/l switch, and additional voltage to headlamps.


Have I done something wrong ???


Help please !


Had been thinking about similar circuit for HEI ... now afraid to do due to above - presently power in at distributer is 0.5 volts less than battery ... is it even worth doing ?


Thanks !!
 
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#6 ·
inner lamps are "aircraft landing lights" and wired completely separately, with separate power source, so are out of the picture.

other than that wiring is exactly as you have shown, with the omission of the inner high beam wiring (is disconnected & sealed).

worked great with engine off.

other considerations: am using a ford relay to power starter. that being said, all connections that were on starter (power distribution) were moved to lug on the ford relay, along with battery cable, & short battery cable to starter, plus charge line from alternator. also at this point there is an 8ga connection to a lug on the left side of the firewall to provide power to msd box & electric fan, (this however, should have no effect on the headlight circuit). at all these points should (excepting minor losses in wire) have same voltage as the bat terminal on alternator since they are all connected together.

off:
battery: 12.55v
power @ ford relay: 12.55v
msd lug: 12.55v
alt batt term: 12.55v

running after run for 5 or so minutes to stabilize voltage from starter draw to battery.

batt: 14.61v (have checked battery before and charging voltage similar)
power @ ford relay: 14.60v
msd lug: 14.60v
alt batt term: 15.00v

curious that alternator has 0.4v higher reading, and 15.00v seems high.

guess should have checked @ headlamp connector also, but didn't.

gotta go out and buy 2 new 80/100 watt h4's tomorrow. don't want to blow them up too.

sure has got me perplexed ! damn thing should work !
 
#7 · (Edited)
"And why is it you have to contradict everything I post?"

You have way too high of an opinion of yourself......... I don't try and contradict everything you post. I do have a different opinion and offer my advice. If you take offense to that ..........

It makes sense to me that differing opinions allow the OP to choose a solution that best fits their skill level and situation.

IMO the output lug on the alt is not same electrical point as the battery. As the alt senses the demand on the electrical system and increases output. It puts the increased voltage/amperage into the system via the wire connected to the battery and depending on the rating and quality of alt, that might spike as high as 16 volts, then level out at 12 to 14-ish volts. When these spikes are dumped into the battery, the battery acts as a buffer and sort of evens out those spikes. So in my differing opinion, making the connection at the battery is a better option than the unstable output lug.
 
#9 ·
You have way too high of an opinion of yourself.........

You're quite right, most Marines do



IMO the output lug on the alt is not same electrical point as the battery.

Really? The voltage at the the positive battery terminal will be identical to the voltage at the out put lug on the alternator as well as the battery connection at the solenoid since they are at the SAME electrical point. Common proven theory.




As the alt senses the demand on the electrical system and increases output.

The alternator doesn't increase anything, the voltage regulator does. One of the reasons manufacturers went to alternators since they, for the most part, provide a steady output as a generator's output varied with speed.




It puts the increased voltage/amperage into the system via the wire connected to the battery and depending on the rating and quality of alt, that might spike as high as 16 volts, then level out at 12 to 14-ish volts.

Increased amperage, really? The amperage rating of an alternator is merely the amount of load it is designed to handle and there is no amperage unless there is current flow. The voltage regulator will not put out spikes unless it is defective, the voltage output will increase as the load or demand increases.




When these spikes are dumped into the battery, the battery acts as a buffer and sort of evens out those spikes. So in my differing opinion, making the connection at the battery is a better option than the unstable output lug.

I doubt that the voltage regulator puts out "spikes" as they would/could be very damaging to other components in the system, therefore any voltage increase/decrease will be a smooth transition. Since the voltage at any given time will be the same at the output lug of the alternator and at the positive battery post how can the output lug be unstable as compared to the positive battery post?
And yes your opinions count just as much as everyone's though in this instance the OP was asking about a specific model and year, namely a 76 Corvette. Do you or have you owned one of these vehicles and if so how familiar are you with the wiring of said vehicle?. I own one and have been through most of the wiring on the car which I feel qualifies me to offer what I feel is the proper and correct opinion.
 
#12 ·
If I offended someone didn't mean to - and you have my apologies. Just trying to correct the problem, and appreciate any help can get.

Cheesy lights - could be, they are certainly old lights, but had no issues prior other than thought could improve voltage & brightness. No matter will have to replace. Don't want to experiment with new ones.

As to landing lights: 13v / 100w - spot beam. If you want bulb #, let me know, will get it from back of bulb. Installation will require minor modification to the bucket. Will have to be wired separately, have too much draw & screw terminals on back of bulb. Have used in ALL 4 headlamp cars owned since 60's, EXTREMELY bright & focused beam, (plus look cool with clear lenses), not that you can see them in a Corvette !

Power to the headlamp relay coils is tapped from the old headlamp power wires, low and high beam, 1 each to the 2 relays. Sorry if was not clear previously.

Used alternator lug as was shortest wire run to the headlamps. Damn it ! - opened up & reloomed the alternator loom.

This leaves the "batt" terminal on alternator & the "lug" for MSD & fan.

I don't really understand, have heard re buffering thru battery, however battery is in rear, if ran separate line direct to battery would be very long and I think would be counterproductive due to length.

If I try to reason this out (no one has ever accused me of being reasonable) seems to me that since all wires go to distribution on the starter relay, in effect are all the same "wire". Unknown by me re location of "sense" wire within the loom. If it is before the power distribution, and needs to be before power distribution, perhaps then that is the problem, as now feed to lights is ahead of "sense" wire connection to loom.

Will have to check re using MSD lug. Is 8ga @ left firewall, approx 2ft long to battery cable on right side firewall. MSD calls for a "battery hot" connection & uses unfused 12ga into box, don't know the draw. Plus the electric fan draws from same lug and is fused for 30amps. Need to find out if 8ga is sufficient size to power both the MSD & fan, --- plus headlamps, for sure don't want to sacrifice ignition for brighter lights.

This all seemed so simple ... and now has me perplexed !
 
#13 ·
You didn't, to my knowledge offend anyone, just a disagreement among members.
I'm enclosing two pages from my wiring diagrams in the hope it will help you find out where you went wrong. It's hard to diagnose from a computer but I suspect that one of the original wires to the headlights is somehow grounded.
I wasn't aware that those lights came in that voltage. I worked at McDonnell Douglas Aircraft in the 60's and replaced a few of the on the fuselage on DC-9's.
 

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#15 ·
I did the headlight relays on my '64 Corvette and housed them in the gutted voltage regulator, which was no longer used with the 1-wire alternator.

Mine works perfectly, increased the headlight brightness by 1 F-stop on the camera, and takes a load off the dash light circuitry brightening those up a bit too.

Unless your alternator is putting out too much voltage, I can't imagine why you would blow bulbs out.





 
#21 ·
Close enough I guess and I've been drawing schematics that way since 62 as that is how I was taught when I was in electronics school in the Marine Corps. They may not be as pretty and clean but they are more precise and eliminate guessing unless I screw up as I did.
 
#23 ·
OP.... if you have a hot cable to the starter, that would be a good place to tie your hot feed into. As far as the sense wire, I'm not 100 percent sure, but I don't think it matters where it's tied into the system. From my understanding, in lay terms, it provides the voltage regulator with a means to compare battery voltage to voltage draw by the electrical system.

If the demand biases below battery voltage, it produces more juice to try balance the off-set, once the bias is above demand, it quits producing juice etc.....
 
#25 ·
The battery in a 76 Vette sits behind the drivers seat which makes it impractical to run wire/s to the battery. Both cables are "0" gauge and the Vette has an ammeter, at least my 76 does, in a shunt circuit which doesn't require 12/10 gauge wire as the ammeters in Mopars of the same era did.
 
#26 ·
"The battery in a 76 Vette sits behind the drivers seat which makes it impractical to run wire/s to the battery. Both cables are "0" gauge and the Vette has an ammeter, at least my 76 does, in a shunt circuit which doesn't require 12/10 gauge wire as the ammeters in Mopars of the same era did."

ntfday.... I have no words for you, Where I suggested the hot connection point was the starter. What exactly are you talking about?
 
#27 ·
In post #7 you referenced the battery as a proper connection point and I still maintain that the battery, starter (solenoid) and the output lug are at the same electrical point and if you can't see that so be it, check it out on a scope. I also suggest that we agree to disagree as this isn't helping the OP one bit.
 
#28 · (Edited)
ntfday, I am done conversing with you on this subject. You are correct the battery and the alt output are at the same electrical point when the alt isn't producing juice.

As I see it, the output lug and the cable leading to the battery are the same potential, however..... if there is a surge in the output of the alt (also known as a spike) then the battery and the output lug are no longer equal, indisputable! As the increase in voltage/amperage travels down the cable to the battery the spike evens out (fractionally) as it is dumped/absorbed into the mass of the battery plates it evens out more substantially, to a point that it's no longer a spike but rather an increase in voltage/amperage, indisputable!

Bypassing the battery as a buffer isn't a sound practice and I wouldn't recommend it to anybody.
 
#29 ·
Same I'm done, but with one thought. If "spikes" as you call them were that prevalent with alternators the manufactures would be having recalls right and left. Spikes do occur, but only with the voltage regulators death throes. Theory hasn't changed but the teaching or understanding of it obviously has.
 
#31 ·
You sir are oblivious to basic electrical theory.


Really? I learned mine in 1962 going through ground radar repair school in the Marine Corps, how about you? I was lead electrical mechanic on establishing electrical power on DC-10's in 1970-72 and did most of the troubleshooting when things didn't work right and I was a tv repairman/quality control inspector at Zenith Electronics in the 80's and 90's and am fairly knowledgeable on EMF and back EMF.
 
#32 ·
Me..... just 30 years as a Military Explosive Ordnance Disposal Technician, Bomb Squad. 12 years Instructing conventional and Improvised Explosive Device dismantling, the last 5 years instructing advanced electronic countermeasures........ and I can spell spike and actually know what it means.
 
#33 ·
Reading wiring has been checked and verified..... Stupid question, the alt been checked...... ?

When I say checked I am saying by an alternator shop not johnney auto zone boy.

Had one go high and cooked a battery, always the other way around, open and no output.

What blows electrical components .... over voltage


Greg
 
#34 ·
If I may...,

The lights on the '76 Corvette take their power from the B terminal on the alternator. At least, that's what the diagrams show. If I were to add headlight relays to bypass the dash wiring, that would then be the place to tie it in as that's where GM does it.

The amp gauge on the '76 is not a "shunt" per say, but like my '64 Corvette is a sensitive galvanometer. It is measuring the slight difference in voltage between the starter terminal and that point in the wiring where the accessories tie in.

Sure the battery, alternator, horn relay, cigarette lighter, etc. are all at the same potential (i.e., positive voltage) but this is only when no load is imposed on the system.

In high current applications, the wiring itself acts as a resistor, enough so such that the galvanometer can read the small differences between these two points.
 
#35 ·
If I may...,

The lights on the '76 Corvette take their power from the B terminal on the alternator. At least, that's what the diagrams show. If I were to add headlight relays to bypass the dash wiring, that would then be the place to tie it in as that's where GM does it.
The wiring diagram that I have shows the power for the headlights coming off the dimmer switch which is powered by the headlight switch.
 
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