Dealing with some charging issues on my 71 Challenger. Mopar Electronic ignition with newer harness. I am running a square back 65 amp alt.

Recently I was driving and the AMP gauge was jumping all over. I found a loose terminal for one of the field wires so I tightened that thinking it was a connection problem. I went out for a drive and about 20 mins in it started showing a high charge. I had the alternator rebuilt and it has the same exact symptom (charge showing high on gauge). Thinking that I fried the Mopar VR, I swapped in a NAPA piece and it did not fix the problem.

I am going to go through and make sure I have good firewall ground (the VR is grounded just fine from what I can tell). I suppose my firewall bulkhead connections could have corroded over time so I will check those as well.

My question is this: Is there anything that could go wrong at the AMP gauge itself that would cause this symptom? I can't check the voltage while driving across the battery terminals to my knowledge. This car has always dipped really low when using the headlights and turn signals (even with an electronic flasher relay). I assume it is not the gauge voltage limiter since the AMP reading is full power, not switched.

Thank you for the brainstorm. I checked old threads but didn't quite get the needed info.