Posting for bro in law: his 72 just developed a problem. When the car's running, no problem, gen light out, all OK. When he shuts the car off, the GEN light stays on. He's replaced the voltage regulator, still doing it. Any ideas?? Thanks!

Sid sounds like one of the diodes in the alternator has gone bad.

I think he might find that the alt.gets real hot real quick when running also.
I agree...bad diode or possibly shorted stator.