Possible voltage issue

[slapstickjim]

But i do want to double check headlight circuit. I put new headlights in and some of the wiring I did fix so maybe I missed something. But when did key bypass all voltage seemed corrected

 

[Mattax]

Voltage only drops where current is flowing thorugh resistance.

Example:
Battery is fully charged.
Engine is running.
Turn the lights on.
We find the Voltage at the battery is the same as at the alternator.

This tells us the wire from the alternator to the fusible links is in good condition.
It doesn't matter if there is only strand of wire left in the battery feed.
That damage is not revealed because the current isn't flowing through it.

But when the battery charging or discharging, there will be voltage drop proportional to the current.
Like this

or another way to check would be with engine off, lights on.

Same thing. In this case the measurement at the alternator tells us there is resistance between the battery positive and where the fusible links join together.

 

[Mattax]

One thing that kind of stood out to me is that you noticed that the lights were going from dim to bright back and forth. Does any other light, say the dome light, do the same thing? Or is it just the headlights? I would check the harness behind the grill and see if there are any grounds to frame on the light circuit. Those radiator support frames can get pretty rusted out if it hasn't been worked/replaced.

You also might be able to isolate the circuit in question by bridging the fuses with a voltage meter/amp gauge or a test light, and see if that points to anything.

His alternator is producing power at 15.4 V.
That's the number one problem.
His bypass still used the body and chassis grounds, so they are OK.
Therefore the main problem is between the bulkhead connections for J1 and J2.
The bulkhead connector itself, the steering column connectors (theirs two) and the key switch are the most vulnerable locations.

It's pretty easy to narrow down checking for voltage drop along the current path.
It could also be multiple locations of resistance that add up.

 

[slapstickjim]

His alternator is producing power at 15.4 V.
That's the number one problem.
His bypass still used the body and chassis grounds, so they are OK.
Therefore the main problem is between the bulkhead connections for J1 and J2.
The bulkhead connector itself, the steering column connectors (theirs two) and the key switch are the most vulnerable locations.

It's pretty easy to narrow down checking for voltage drop along the current path.
It could also be multiple locations of resistance that add up.

So all reading im getting should suggest wiring good in engine bay?
So what I been doing is narrowing it down to bulkhead inward corect?
My numbers I gave with key bypassed. That would be a normal healthy reading?

 

[DartDave73]

His alternator is producing power at 15.4 V.
That's the number one problem.
His bypass still used the body and chassis grounds, so they are OK.
Therefore the main problem is between the bulkhead connections for J1 and J2.
The bulkhead connector itself, the steering column connectors (theirs two) and the key switch are the most vulnerable locations.

It's pretty easy to narrow down checking for voltage drop along the current path.
It could also be multiple locations of resistance that add up.

I don't know. Maybe it's something as simple as a bad battery. It could be a source of resistance causing the VR to react. It's just hard to troubleshoot where I sit. It's a lot easier being there. I can offer suggestions but it's the nature of electrical. Process of elimination. I wish I could be of more help here.

 

[slapstickjim]

I don't know. Maybe it's something as simple as a bad battery. It could be a source of resistance causing the VR to react. It's just hard to troubleshoot where I sit. It's a lot easier being there. I can offer suggestions but it's the nature of electrical. Process of elimination. I wish I could be of more help here.

I have my grill out. Come stop over

 

[Mattax]

Maybe it's something as simple as a bad battery. It could be a source of resistance causing the VR to react.

Explain that.

 

[DartDave73]

Explain that

It's like an internal "short" in a battery. Where the battery trips the VR to charge where it's needed or not. It doesn't happen very often. I'm throwing out possibilities of things that can happen. Sometimes the simple and obvious gets overlooked.

 

[Mattax]

It's like an internal "short" in a battery. Where the battery trips the VR to charge where it's needed or not.

Sorry I still don't get it.
If a battery is shorting its going down a cell and won't charge properly. Don't see how that the regulater.

 

[DartDave73]

Sorry I still don't get it.
If a battery is shorting its going down a cell and won't charge properly. Don't see how that the regulater.

It usually happens on an old battery. Specially one that's not a "maintenance free" battery. Water is sometimes added, if it's not distilled water (usually not) it can introduce stuff like minerals and things that can bridge across plates inside of the battery. The cell just doesn't have to "fail" completely to be a problem. It's a battery. Just like anything: If it's made by human hands, anything can fail.

 

[DartDave73]

I don't rule out anything when it comes to electrical issues. Electricity has a path it follows. That path can be interrupted, delayed or misrouted. Batteries are a part of the charging circuit. It doesn't play any part of the charging process except to hold a charge. But the alternator will be signalled if that battery is showing low. If I'm wrong then take the battery out of the picture and see what happens. Can't do that. Because it has to be there, in function, to provide the extra "push" to the system on demand. I never rule out a bad battery. Fixed issues because of them going bad. Is it very common? No. Is the problem fixed yet? So don't rule anything out.

But when it all comes down to it, process of elimination, check the obvious first, and don't rule out anything. Especially new parts. But that's the nature of electrical issues. It's never fun. But it feels good when solved.

 

[Mattax]

It does not have to be a process of elimination.
Stuff like this is straight forward diagnostic following the current flow.

As far as taking the battery out of the circuit, that's a shade tree method that was all too common.
Disconnect the battery and if the engine keeps running they know the alternator is working.
There's a number of problems with doing this but it often works. It can cause spikes that can damage transistors. But people who do it don't really know much about what they are doing. As often it doesn't work and they think its the alternator failing.

In this case Jim's experiment where he bypassed the interior wiring showed the battery has nothing to do with the high voltage.
His measurements show there is resistance in the path between the Bat terminal and the Field terminal.
Put the two together and the problem is between the bulkhead connection for J1 and J2. A few more measurements and he'll know more precisely. Hate to see anyone unwrapping wires and replacing parts that are fine. He got about halfway there but took some sidetracks. I'm trying to help him understand how track it down so he's not taking any more sidetracks.

 

[DartDave73]

It does not have to be a process of elimination.
Stuff like this is straight forward diagnostic following the current flow.

As far as taking the battery out of the circuit, that's a shade tree method that was all too common.
Disconnect the battery and if the engine keeps running they know the alternator is working.
There's a number of problems with doing this but it often works. It can cause spikes that can damage transistors. But people who do it don't really know much about what they are doing. As often it doesn't work and they think its the alternator failing.

In this case Jim's experiment where he bypassed the interior wiring showed the battery has nothing to do with the high voltage.
His measurements show there is resistance in the path between the Bat terminal and the Field terminal.
Put the two together and the problem is between the bulkhead connection for J1 and J2. A few more measurements and he'll know more precisely. Hate to see anyone unwrapping wires and replacing parts that are fine. He got about halfway there but took some sidetracks. I'm trying to help him understand how track it down so he's not taking any more sidetracks.

Ok. You know best. I've been working on vehicles since the 80's, but hey, I might need a few more years before I get it. I'll just drop back on this post and let you handle it. You seem to know what's going on. Just ignore what I said. I am a potato.

 

[slapstickjim]

On the positive note. The so called sidetracked. I have a new regulator on my shelf, 3 others I now know work fine. An extra alternator that works. I now know every wire in engine bay is good. And will be newly wrapped in electric tape. I have now some cool charging diagrams printed out. And I accomplished a steady 14.6 volts.

I was very careful and meticulous back in Feb under my dash. Dash wiring should be not the issue. I'm thinking ignition which is in said circuit.

But that will wait till next week. Tomorrow is Sunday and it's a no work day here.

Wait you say halfway. Uggg another 7 hours to go baha

 

[slapstickjim]

Ok. You know best. I've been working on vehicles since the 80's, but hey, I might need a few more years before I get it. I'll just drop back on this post and let you handle it. You seem to know what's going on. Just ignore what I said. I am a potato.

Potato potato I like both. And batery was on my list but after i hotwired and voltage was fixed. No need and I was looking at ground and lights. But again voltage fixed at hotwire. So to me everything says bulkhead in. But
Ights still my do list just because some connection concerns but not urgent. So to me everything you suggested was not crazy. And thankyou.

Thank you both of you. I keep update when get back at it.

 

[Mattax]

I was very careful and meticulous back in Feb under my dash. Dash wiring should be not the issue. I'm thinking ignition which is in said circuit.

Wait you say halfway. Uggg another 7 hours to go baha

Since you did the interior wiring, maybe its right at the bulkhead.
I think you can find it pretty quick if you use the voltage drop method and not have to unwrap everything.
The switch is certainly a candidate.
It could be something really simple like a terminal backing out of the connector when the housings are squeezed together.
Barb damaged or plastic worn, or just not pushed in 'til it clicks.
I have had that on both a Ford type coil connector and a GM SI alternator connector. Found the latter when backprobing for a voltage reading. There's been others but those two stand out in my memory because the intermittant dying was a serious issue and the intermitant charging was driving me crazy trying to track down.

 

[slapstickjim]

So I think I got it.

The wires at bulkhead are clean and tight. So I moved in alil further. First unhooked everything I installed (tach, radio, gauges) and nope 15.7 at baterry. Rehooked all that up and pulled untaped wire harness enough to work at. Un hooked all steering column plugs. All wires but one looked good, seemed tight and clean. A black that seems to feed accessories fell out of connector. So I ran a jumper at steering column wires between j1 and j2 started car and 14.6. So bulkhead is good . I plugged it all back in and that black wire def clicked in place. Started it and 14.6. I grabbed the connectors pulled pushed smacked with players, jiggled and stays at 14.6.

Is that a good number?
Nothing seemed odd when I unplugged them
(Accept that one wire) any thoughts?
Did that fix it?

 

[Mattax]

Not really sure what you did. The only black wire in the drawing is for the brake lights

If its a the same V at all feeds and at the sense terminal then you got it.
Add some load in the path if you're not sure.
I don't have a full 76 manual so can't say what the acceptable drop was for that year, and its too different to say its going to be the same as earlier models. A few tenths difference would be OK for sure. Over 15.5 was just asking for trouble.
Now see if the headlights work as they should. Could have been the breaker tripping due to the high voltage causing the lights to draw more current.

If you can get the ammeter to work, then you could see what the battery is doing.

if you want t o monitor voltage while in the car, there are USB port/Voltage gages that can be placed in the cigar lighter. My experience so far with one is that it seems to be somewhat accurate. Would need to check the diagram to see if its turned off with the key in '76. I wouldn't leave it in all the time anyway.

 

[slapstickjim]

Def getting some books for this car (electric, mechanics etc.)

Looks like my plugs except there was one more all coming out of steering column. That top plug q12 bk was one that was not completely in. When messing with it it was shutting heater fan and radio off when I pulled just black wire out. I cleaned it and pushed it in and I clicked and seems tight now.

I installed after market gauges and volts show hair under 15. And tested it all over seems 14.7 ish all over. Even had headlights on, door open, radio on, heater fan on and wipers. Seemed to hold 14.7ish all over.

Should have checked under dash first lol. Not sure what I did to fix it but no complaints.


Can't thank you enough for those diagrams, helped me trace wires for sure.

Next up get it all taped back up and drive it at night. See how light behave.

 

[Mattax]

Looks like my plugs except there was one more all coming out of steering column. That top plug q12 bk was one that was not completely in. When messing with it it was shutting heater fan and radio off when I pulled just black wire out. I cleaned it and pushed it in and I clicked and seems tight now.

I'm sorry I missed that. Maybe ther terminal not quite fitting effected the connector s othe J2 wasn't tight.
You have it right Q is accessory.
Q1 was for electric tailgates and convertable tops. Q2 was switched accessories, Q3 was for fuses that are always hot.

I installed after market gauges and volts show hair under 15. And tested it all over seems 14.7 ish all over. Even had headlights on, door open, radio on, heater fan on and wipers. Seemed to hold 14.7ish all over.

The '76 wiring strategy should minimize resistances so not too surprised.

Its still a long route to the headlights, and they still only got 18 gage wire. If you drive at night, look into doing a relay harness. The Kioto headlight and relay harness from Toyota is still a great deal if you don't mind a little bit of customizing to fit your car. They are sold for Toyata Land Cruisers that originally came with sealed beams. You can find some recent threads about them.

PS> The specs for the '76 alternator suggest to me that it is the new 'revised squareback'. It should work well but has a higher field current draw than earlier models. The original VR I'm sure can handle it.

 

[Mattax]

Not sure what I did to fix it but no complaints.

You eliminated the resistance.
Think of current like a river.

I wrote a little more about working with electricity recently. See if either of these is helpful

Post in thread '76 318 Duster barn find?'

Mar 28, 2026

Love those rims.

OK. Working backwords

So, what if anything do I need to do to make the bulkhead connection safe and not have to worry about fires.

In most cases I would say stop worrying. Most of this is chicken little, and some percent is real but self inflicted. I can post you some links (no pun intended) a bit later.

Now in your situations, because of the conditions it will certainly be worth going through the wiring and checking on the condition and making repairs. Ignition requires heat and combustibles. So a poor connection or damaged wire is resistance and resistance...

• Mattax

This one too, even though its a slightly different wiring strategy it may help illuminate the concepts

Post in thread 'Starter clicks using the key, engine starts by jumpering the relay'

Mar 19, 2026

I thought you bought a new harness?

There always should be system voltage at both ammeter studs, at the stud on the alternator, etc.

So if during the start the voltage at the battery drops to 11 V, then the voltage at the alternator stud should be 11 V.

Key in start draws maybe 5 to 8 amps through the ammeter. (I'm assuming here that the '74 E-body has a similar system to the '70, and not a shunted ammeter.)
There should be 0 Volts across the ammeter studs with 5 - 8 amps though it, but .25 V is small enough not to generate heat.

An easier test for...

• Mattax

 

[slapstickjim]

Ok it's not right. Ate supper went back out and 15.2. Ugggg. Unplugged all column wires and jumped j1 j2 again. Like 14.7 but interior light goes dim bright dim bright and volt gauge has a lil bounce to it. Sort of tune to the light dimming. Might have did that earlier but the sun was lighting up garage very brite. I plugged all column connectors back and yep 14.6 and head lights, dome light and gauge all are on same tune. But voltage seems ok. Like earlier. Any thoughts. Been a .long day so I'm not looking at her again Tonight.

 

[slapstickjim]

Ok update I been busy on this car, first testing electric is not my strong suit. I can wire a house change outlets but comes to ohms resistance formulas I can get lost real fast.

Refresh
this all started when I drove at night and headlights were going dim bright dim bright dim. Tested voltage at battery 15.7.

Mattax here gave me some helpful advice and used it best I could. Thank you.

First trial
I tested like he said battery 15.7. // R1 15.6. // blue wire 14.3 // green wire 10.7. Tried dif reg, grounds, alt ,ground reg. And stayed same.

2cd trial
I unhooked 2 bulkhead connector And jumped j1 and j2 and screwdriver on starter relay. Battery 14.6 // R1 14.4. // blue wire 14.24 // green wire 9.3

Long 3rd trial thinking it's bulkhead, steering column
Un taped First 10 inch of wire and all looks good from bulkhead. Unplugged steering column completely and looked good than came back 10 min and it acted weird. I started thinking since I'm in the car I now notice the dome light doing that dimming thing. And the volt gauge was bouncy to the same done light rhythm.
Un bolted bulkhead pulled it down away from brake so I see better. Found 1 of the j1 wires a lil loose so I removed it and got it to back in tight. I then did all the wires seeing I had it out anyway. So bulkhead is def great now. ( this winter I installed tach, gauges, radio all with simple plug in to factory plugs) so i unplugged everything I installed no change at this point I was concentrating on that dimming light and occasionally probing at batery for volt. Totally unooked steering column again and jumper j1 j2 nothing changed. Removed speedo cluster to see if a wire was pinched in there.nothing changed. Everything I checked at battery seemed to be around 14.7. But that dimming domelight was making me nuts. With car running I removed each fuse no change.
So I was thinking what's making that pulse. Is the regulator realy ok?? So I put a new one I had on and rerun the ground I put on the other day. And bingo. Dome light is steady on no volt gauge bouncing. Hooked everything back up except speedo cluster car starts with key (was getting used to my Mr t hotwire skills) and no domelight dim and gauge looks great. Couldn't checked headlights do to cluster on back seat.

Now Battery 14.86 // R1 14.85 // blue wire 14.46 // green wire 8.56 but now dome light and aftermarket volt gauge settled.

I can't go back what i should of done but maybe first ground for reg was not good ugggg

So what do you think?
Should I put cluster back in and claim victory?

 

[superchargeddrt]

The voltage regulator needs a clean non fluctuating voltage on the blue ignition wire. You might have dirty contacts in the ignition switch. Ive seen this cause issues like the flickering headlight syndrome. I use a relay to supply the power to the voltage regulator ignition wire. This might cure your problem.

 

[slapstickjim]

The voltage regulator needs a clean non fluctuating voltage on the blue ignition wire. You might have dirty contacts in the ignition switch. Ive seen this cause issues like the flickering headlight syndrome. I use a relay to supply the power to the voltage regulator ignition wire. This might cure your problem.

But I had steering column completely unhooked and domelight was diming