No Power to anything
We had a bad connection at the Bulkhead Connections on the Firewall side of a 67 Corronet R/T doing the exact same thing.
As you are looking at the bulkhead from the front of the car, wiggle the wires at the lower left of the bulkhead on the firewall side with the driver's door open. As you are wiggling the wires see if your dome light comes on. When the dome light comes on this is the wire connection that you should clean up and reinstall. We squeezed the Female part of the spade after cleaning it up and cleaning up the spade to help hold it tight after we slipped it back together. All is well now on this one, and that was last Summer. All is Good . . .