1982 Corvette turn the headlights on and the amp gauge goes all the way down to the negative side. If you turn the dash lights off it come back up to where it should be? What is the problem causing this?

 

ED
I would be looking @ the head light switch 1st, when the amp meter goes - it means 12 volts power to ground = that's not a good thing something is shorted.
Also there is a relay in that circuit too, it should be checked.
If you are not familiar with electric especially cars, take it to a PRO or someone who is.
12 volts shorted to ground can cause a fire.
The more I think about it change the head light switch

 

Well- first of all the 82's had Voltmeters NOT Ammeters- In 75 was when GM went to the Voltmeter.

First-

When you turn on the headlights- do they work fine AND the voltmeter goes to zero?

If so- what happens when you turn on the interior lights w/ the headlight switch?

Let us know-

Richard

 

When the headlight are on the volts go all the way down if I turn the dash light dimmer off the volt meter comes back to where it should be on the gauge. The battery and alternator were both tested and are OK. I don't if the problem is in the printed circuit for the gauges is bad? I didn't see any broken or burned spots on it. Could it be a bad headlight switch?

 

What happens if you turn the headlights on dash lights off and turn on the heater fan on does the gauge still show 14 volts charging?

Pete

 

When the voltage goes down, is this with the engine running or off?

 

Sounds like a bad ground on the cluster... As the Voltmeter and gauge lights share the same ground.

Richard

 

The headlamps are "hunting" an electrical ground and have found another route that overwhelms that circuit. Run a temporary ground to the headlamps (use jumper cable, house extension cord, etc); then, with headlamps ON, see what the voltmeter is doing. If it reads OK, then find where the [factory] headlamp ground is lost and repair it.

 

Bad ground on the cluster or the ground for the gauge has somehow got jumpered into the power for the cluster lights. Either way, the gauge is grounding through the cluster lights so when you put power to the cluster lights the ground for the meter becomes 12V and with the same voltage on both sides of the meter it reads 0V.

 

have you been working in the dash?? or any where on the car when this started?? need some history to help.

 

Yes
Running

 

Yes

Running

 

Is the ground in the printed circuit on the back of the gauge cluster?

 

YES and NO....
Here you go-

Voltmeter is the lower left. I see grounds for the gauge lights on the right side through the top right connector- but for the left side gauge lights -it looks like the voltmeter is grounded to the gauge case.

So you might check and see if the gauge case - or the connector on the top right is grounded.

 

Just run a temporary ground to the headlamps and then see if the problem goes away. That's the simplest test to check out the problem.

 

Looking from the back of the cluster, there is a ground wire 4 down from the top on the left or voltmeter side of the connector. Should be a black wire with a pink wire directly above it and a brown directly below it.

The circuit trace from this wire goes to the bottom bolt on the fuel gauge. This wire grounds the bottom bolt on the fuel gauge and in turn the bottom bolt on the fuel gauge grounds the steel cluster shell.

The bottom bolt on the oil pressure gauge is connected to the cluster shell to ground that gauge.

The left bolt on the voltmeter is grounded to the cluster shell to ground that gauge. It also connects to another trace that grounds 3 instrument cluster bulbs surrounding the voltmeter and the clock.

This means the oil pressure and voltmeter gauges as well as 3 cluster bulbs all rely on the fuel gauge connection to the cluster case and then to the ground trace. So, following the failure, if your fuel and oil pressure gauges always work, then that means they are grounded and the cluster case is grounded. So, I would suspect the connection between the bolt on the voltmeter and the cluster case. The meter is likely using the 3 cluster bulbs as the ground instead of the case.
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