Hello all, I would like to know if somebody would tell me if I can diagnose the voltmeter on my 77. First, everything all good with the alternator. I got my 14.3 volts at the battery while engine running and 12.6 volts when not. Checked for voltage at the gauge terminals themselves and I got the same reading as the battery. Bought new gauge thinking must be the gauge itself. Wrong, new gauge, same problem. No readings from the gauge even if I got the voltage at the terminals. Checked gauge with seperate wires at the battery while engine running, gauge indicate approx same readings has with the multimeter. Replaced circuit board after damaging it by mistake. Now, because I've been playing with the old gauge and the new gauge so much I don't remember which resistance is the one going with which gauge. What should be the ohm readings through it? Anybody has a clue why the power is right there behind the gauge but gauge not showing anything but if I test the gauge out of the car it's working??? I'm confused Testing the resistance, I think one of them is not good anymore. They should have the same reading, one has some resistance (47ohms) if I remember, the other stays at 1(open)= (broken) Also what would be the cause of the needle going back to zero if I manually move it to 18volts and let it go. That's in the car gauge plugged in, car running. Many questions... not too many answers. Tks

 

I don't know what the ohms are supposed to be, but if it works hooked up directly to the battery and not through the harness, I would suspect the harness is not giving it the battery voltage or a ground.

 

Thing is Myk7, I do have the voltage at the gauge through the harness. I have the same reading as the battery right on the screws behind the gauge. So the ground/power is going through harness -> then circuit board -> and connected to gauge but the gauge itself is not showing any readings. That's why I do not trust the ceramic resistance but do not know what would be the symptoms if it was the case.

 

When you are checking the voltage on the harness at the gauge, where are you grounding your meter? On the other connector at the harness, or on some metal part under the dash? You need voltage and ground for the gauge. If the harness lead isn't getting to ground for some reason, the gauge won't register.

 

LB, my gauge is in the console, printed circuit and all. I touch right behind the gauge on the 2 screws that have "wiring" going to it through the printed circuit. When I do that, I have the readings coming straight from the alternator. Car running was 14.6v. One of these screws got to be the ground right? The other is power. The last screw, which has the other end of the resistor is not contacting anything except the resistor. I just tried it again tonight. Took gauge out of console and tested seperately. It's all good. Am I suppose to put my multimeter leads somewhere else? Tks

 

It sounds like the ground side of the circuit is open. Run a temp. lead from the neg. side of the meter to ground and it should work.