[VetteVet]

There's a junction block on the passenger fender by the battery where the 12 volt feed wire from the battery joins with another wire that goes to the firewall junction block by the master cylinder. Take this wire off the junction block and clean all the terminal ends and the junction block and see if that helps.
Also another source of trouble is the external voltage regulator wire terminals.Clean those also and make sure the small wire that grounds the regulator to the radiator core support has a good connection.
There's probably a dozen other causes for this problem but these are two common ones.