Voltage drop on gauge

[popeye1978]

A lot of great information here, helps explain why my own voltmeter is indicating low & adds to the list of projects (learn more electrical!). I'm running one of these guys on the cigarette lighter as "the" gauge:

https://www.amazon.com/dp/B0773BYS6P/?tag=gbody-20

 

[Bri guy]

A lot of great information here, helps explain why my own voltmeter is indicating low & adds to the list of projects (learn more electrical!). I'm running one of these guys on the cigarette lighter as "the" gauge:

https://www.amazon.com/dp/B0773BYS6P/?tag=gbody-20

Is that accurate to whats at the battery and alt?

 

[fleming442]

What I'm seeing through the magic interwebs is that the body ground underhood is weak or missing. Once restored, the whole system should improve: brighter lights, etc.

 

[roger1]

Is that accurate to whats at the battery and alt?

The cigarette lighter is on another circuit than the voltmeter. Like I said earlier, there are 2 wires that feed 12+ to the main fuse panel. One of them splits and goes to both the fuse panel and the ignition switch. And the ignition switch (when in the on position) will feed 12+ IGN power to the circuits back at the fuse panel. This is where the voltmeter gets it's power. On the other hand, the cigarette lighter 12+ comes from the other panel feed wire. That one also supplies power to the taillights, horn, clock and interior lights. The voltage drop at the lighter is likely to be significantly less than at the voltmeter. And like I said earlier, there is a lot of voltage drop that happens in that floppy circuit board alone. Voltage drops are caused by current loads and resistance in the circuit.

Btw, I'm getting this info from the wiring schematic from the factory service manual for my '83 El Camino. I'm only assuming your wiring is the same as that too. You would think all G body cars are wired very similarly.

 

[pagrunt]

Btw, I'm getting this info from the wiring schematic from the factory service manual for my '83 El Camino. I'm only assuming your wiring is the same as that too. You would think all G body cars are wired very similarly.

From what I've seen in my factory wire diagram books for '78-'80 & what's in my '81 service manual the wiring is close to 99% same. Even my '86 MC parts dash harness is almost the same as my original '81 MC one. There will be some minor model year changes, the change in the bulk head plug about '84, the relocating of the flasher fuses, the addition of the computer related wires starting in '80 on some models.

 

[roger1]

What I'm seeing through the magic interwebs is that the body ground underhood is weak or missing. Once restored, the whole system should improve: brighter lights, etc.

Yes, that ground wire definitely should be checked. They often get frayed and break. Without the wire, the body gets it's ground through the motor mount bolts and then through body mount bolts. Not a good situation.
Glad you brought this up though for another reason too. This is also a place where the factory did kind of a bad design. That small wire is only 12 gauge and mounts on the fender. Another source for a voltage drop in every circuit of the car. I did away with that wire an installed a short section of 4 gauge wire underneath that goes from the engine block to the floorboard. And another short 10 gauge wire from the engine to the frame. Then any custom wiring you do, you can get a good reliable ground from any point on the frame or the body.

 

[Bri guy]

What I'm seeing through the magic interwebs is that the body ground underhood is weak or missing. Once restored, the whole system should improve: brighter lights, etc.

I wouldnt doubt that im missing a ground somewhere. This car has been engine swapped

 

[roger1]

I wouldnt doubt that im missing a ground somewhere. This car has been engine swapped

It would only take you a second to look at the 12ga ground wire from your battery to the fender and see if it's OK. The other ground wire is the large one from the battery to engine block. Since the car starts, we know the big ground wire is OK. That's it, there are no others. So even with the fact the engine has been changed, there is nothing else to look at there for missing grounds.
As far as bad or missing grounds in your dash wiring, the most likely culprit is at the slip fit in connector to your floppy circuit board. One of the contacts is ground and sends a ground to each bulb and gauge. Each point is subject to a high resistance connection from degradation and tarnish on that circuit board just the same as the positive wire connections.

There is only one ground source under the dash. A black wire attaches to the metal dash frame with a star washer. If that ground is missing. Nothing at all in the dash would work. If it was loose, everything would go out intermittently. So, if voltage reads low and bulbs are not bright, the culprit is the connections on the floppy circuit board.

 

[Bri guy]

It would only take you a second to look at the 12ga ground wire from your battery to the fender and see if it's OK. The other ground wire is the large one from the battery to engine block. Since the car starts, we know the big ground wire is OK. That's it, there are no others. So even with the fact the engine has been changed, there is nothing else to look at there for missing grounds.
As far as bad or missing grounds in your dash wiring, the most likely culprit is at the slip fit in connector to your floppy circuit board. One of the contacts is ground and sends a ground to each bulb and gauge. Each point is subject to a high resistance connection from degradation and tarnish on that circuit board just the same as the positive wire connections.

There is only one ground source under the dash. A black wire attaches to the metal dash frame with a star washer. If that ground is missing. Nothing at all in the dash would work. If it was loose, everything would go out intermittently. So, if voltage reads low and bulbs are not bright, the culprit is the connections on the floppy circuit board.

Ok. Awesome. I know for a fact there isnt one on the fender. I will put one on and see what happens.

 

[pontiacgp]

GM didn't seem to put much thought into the grounds in these cars.......