1972 Plymouth scamp charging and grounding issue

Reminds me of an old friend and his Chevys. First a 68 Nova that repeatedly lost alternator, voltage regulator, or both. I grabbed the battery ground cable and pulled the wire right out of the lug that was bolted to the block. Found and fixed.
A few years later and his 8? Chevy pickup. Big dist' with coil mounted on top.
The large red wire going to the BATT terminal on that thing wasn't properly routed and had a tiny chaffed spot where it would short to the intake manifold only after everything got good and hot. He could drive it work and back without issue. Head into town and it would die in the street. Get it started again and charging system was gone. By the time I got hands on it the fault was easily found. That wire was melted all about under the dash. Anyway...
In your case, I would be checking battery cables ( Positive all the way to the starter ), white engine harness connector at rear of right valve cover, white connector to ignition switch under steering column, and wiring to any aftermarket addons such as stereo.