1972 Plymouth scamp charging and grounding issue
First things I'd try
1.......As others have also suggested, inspect and retighten grounds from battery to engine, to body, etc
2.....Dismount the voltage regulator. Scrape the mounting and firewall clean around the bolts and re-mount using star lock washers. It MUST be tight and grounded. Do the same with your electronic ignition
3.....To get a "start" on looking for voltage drop, and because this is intermittent, try this one thing. Make up a good heavy clip lead, say, at least no14 or better no 12 wire. Turn the key to "run." Probe the ignition ballast to find the highest reading. This is the "key side" of the ballast. Get an adapter spade connector if necesary. I can't find a photo, similar to this:
With the car started and running, and your adapter in place on the ballast, hook your jumper wire from there to a battery source, such as the big stud on the start relay. This effectively hot wires the car, and guarantees a solid battery connection to the ignition buss.
See if that settles down the charging problem
First things I'd try
1.......As others have also suggested, inspect and retighten grounds from battery to engine, to body, etc
2.....Dismount the voltage regulator. Scrape the mounting and firewall clean around the bolts and re-mount using star lock washers. It MUST be tight and grounded. Do the same with your electronic ignition
3.....To get a "start" on looking for voltage drop, and because this is intermittent, try this one thing. Make up a good heavy clip lead, say, at least no14 or better no 12 wire. Turn the key to "run." Probe the ignition ballast to find the highest reading. This is the "key side" of the ballast. Get an adapter spade connector if necesary. I can't find a photo, similar to this:
With the car started and running, and your adapter in place on the ballast, hook your jumper wire from there to a battery source, such as the big stud on the start relay. This effectively hot wires the car, and guarantees a solid battery connection to the ignition buss.
See if that settles down the charging problem