I went for a brief cruise in my '66 coupe this week. It was daytime so lights weren't on nor was the radio, but I noticed the volts gauge acting weird, spiking down for a bit and then back to normal. Went to start it up yesterday and the solenoid only gave a clicking sound, engine did not turn over, and then nothing at all. I keep it on a trickle charger as it's not driven much, so my first thought was the battery. It's about 3 1/2 years old and it tested as marginal so I replaced it. Installed the replacement and it fired up immediately. I came back to it this morning and solenoid was clicking again and the engine not turning over, and then nothing. The battery charger shows it as fully charged. Terminals are clean and tight. Grounds are good. It has an updated Painless harness and all connections seem good. The alternator is just a year old. That would seem to suggest either the solenoid or the starter as the culprit. Suggestions for tracing or testing?