1980 Voltmeter low reading

[Dana A.]

I recently purchased a '80 L-82, when I brought it home I noticed the volt gauge was reading around 9V. I metered out the battery, it read 12V+ with the engine off, and 14V with the engine running respectively.
I figured it must be a bad gauge and replaced it with a new OEM Delco gauge, when I first put it in it read 14V, with the engine running, it then went back to reading around 9V.
If there is any load (A/C, lights, etc.) it really tanks the gauge.

What would cause an erroneous reading at the gauge?
I have no reason to believe the battery or the alternator is to blame, as the voltage readings are where they should be with the engine off, and running.

Thanks for your help

[Richard G.]

Re: 1980 Voltmeter low reading

Like all things electrical good troubleshooting practices are required.
Get out the schematics and first prove the gauge and work backwards.
Sometimes there are "common failure points" that can be addressed without the leg work.
However it is usually a time consuming pain. It is also the one thing that fixes it every-time.
Rick