C3 79 gauge or charging system

[David L.]

The problem started about 3 years ago. The volt gauge needle at mid rpm and highway speed stays all but pegged all the time even if I charge the battery. As of last year along with showing a max charging the needle also wildly bounces across the scale at idle but not above 1500 rpm. so I’m sure most of you are saying ( Bad Gauge ) but one more strange factor. If I turn on the interior courtesy lights they flicker at the same rate as the needle does bouncing on the gauge as well as the under hood light and I guess all lights. I have checked all the body grounds, I have replaced the regulator in the alternator, no change, I even tried bolting on a rebuilt one just to see if there was any change and there wasn’t. I thought I found the problem on the circuit board of the gauge cluster where it at one time was repaired, so I replaced it, still no change. I checked the output of both my original alternator and the aftermarket one with a digital volt meter and both showed about 14.56 volts at the back of the alternator and about 14.25 at the battery. If I shut off the car and check the dash gauge with key on and engine off it shows about 13-14 volts on the gauge.
Any ideas where to look next ?

[Verle R.]

Re: C3 79 gauge or charging system

Dave,

Is the alternator in stock configuration, as in not a one wire?

I am not specifically familiar with the 79 charging system so I will give some generic ideas.

If it is not a one wire the alternator has a sensing wire to determine the need for charging and has an exciter wire supplying 12 volts to activate it.

It is a fairly common problem for either or both of those wires to be loose in the plug that plugs into the alternator. Corrosion or just people pulling on the wires can cause the problem. If one or both are loose they could be making erratic contact.

Another location to check is the power distribution point. This is the place in the wiring harness where the sensing wire from the alternator connects into the wiring harness. I do not have a wiring diagram of a 79 so I am not sure where that point may be. Later C3's have a junction block in the battery compartment near the battery. Check it also. That may or may not be the sensor connection point.

Check where the charging wire from the alternator hooks to the car.

Loose connections at any of those locations can cause erratic operation of the charging system.

Verle

[David L.]

Re: C3 79 gauge or charging system

The alternator is original to the car, electrical wiring is stock too. It is a low mileage car.

I thought I may have found the problem last night when I pulled the 2 wire clip off the back of the alternator. Found a fair amount of corrosion on the one terminal. I cleaned both pins and applied some dielectric grease….still a problem.

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