I replaced the AC compressor in the 1964. I painted it too well and when I put the ground battery cable into it via the bolt that holds it on, the car refused to charge, probably due to poor contact with the metal. It occasionally spiked up, but rarely.
I relocated the battery cable to be secured by the bolt that holds the coil onto the intake manifold, and used a wire wheel on ALL surfaces involved and am certain that I have a good metal-to-metal connection.
The alternator gauge immediately showed results, reaching for "C"harge and away from "D"ishcharge immediately once I was off idle. Woked great the day that I drove the car after performing this correction.
I go to drive the car today and it is displaying identical symptoms as before. When the lights are on it is at the mark half way between the center and "D", meaning that the battery is draining. Driving the car at freeway speed results in the needle creeping to the center but never over, and varying depending on the electrical load and RPM put on it. It moves up as the engine spins faster, but again, never into the charge area.
I am beginning to suspect the voltage regulator and plan to do that next. Any reason to do otherwise? The car has 27,800 miles (!!!!) and sat forever but is very clean.