electrical problems--help please

[mobilenuke]

Just purchased Superformance136 with a 1963 427.
After a very hot (110) day of driving eveerything seemed fine. Took the wife out for a ride last evening and noticed that the ammeter was on the - side.
After I turned the lights on it dropped even further.Pulled in to get gas and unable to start after. After a jump drove home with lights and ammeter still on
neg side. Pulled into garage and turned off car, tried to restart and battery not able to revive the beast.
Went out today, pulled battery and had it checked, before trying to remove alternator, and it tested as just needing a charge. Took it home, reinstalled and turned on the key----started right up? Ammeter reading on the plus side with an increase when revs up even when lights on. Engine temp goes up to proper operating temp and ammeter drops to 0 then drops to the neg side
Sorry for the long winded explanation but my question is--- could it be the electronic voltage regulator or possibly the altenator?
Jeff
PS tried to start car when it was at temp and no go---won't turn over