Overcharging

This "sounds" like a classic case of voltage drop in the harness or ground, a subject I've posted many times

To check this, get your voltmeter as close as you can electrically to the VR. The ballast resistor power, or the blue alternator field wire are two points. Don't disconnect anything, leave all wiring connected "normal." Put the key "in run" with engine stopped. Stab one probe into the battery POS post, and hook the other to the power at the ballast. You are hoping for a VERY small voltage, the lower the better. Anything over about .3V you need to look into

The functional path in a stock harness is battery...starter relay stud...fuse link....through the bulkhead connector (RED ammeter wire) through the ammeter, out the ammeter on the BLACK ammeter wire, to the WELDED splice.....and branch off to the ignition switch connector.......through the switch......out the switch connector on the blue "ignition run" line....out the bulkhead connector.......and to the underhood loads, that is ballast, VR, alternator field, and depending on year model, electric choke and one or two smog doo dads.

The usual suspects are the bulkhead connector terminals, the ignition switch and the connector