Dead delta help please
 

Hello all
I have a 1969 delta 88 convertible 350 rocket.
After 1/2 hour hot city driving engine / lights /radio and most electrics shut down. Engine is NOT overheating. 15-20 minutes electrics return and motor fires up. I have had it checked 3 times. New ground wires installed. Battery checked. Priest performed Gremlin exorcism-- no results please help