I have 83 z28 all my gauges work properly except the volt/battery gauge. It’s not pegged out it sits below 8 volts. Car runs fine so I know it’s just a wiring issue but not sure how to trace the wires down. It has a plug on the alt with red and black wire. Red wire runs to the output on the back of the alt. The black wire runs into the wiring harness. And a wire from the back of the alt to the positive side of the battery. Is it the black wire that is bad?

 

No, it's not the black wire, or any other wire near your alternator. Your volt gauge doesn't have wiring running directly to your alternator. As long as all of your other gauges work, it's a 100% certainty that your voltmeter itself is defective.
Look at this wiring diagram, see how your voltmeter is powered in parallel with your other gauge's + and - 12v supply? That right there shows you that if your other gauges work, and the voltmeter don't, it'll be the voltmeter you'll be needing to replace....

 

Thanks for the response. That makes sense.