Here's the voltage regulator, not NOS but an original that has been remanufactured. I've gone through 5 AMK voltage regulators and none have worked. I dropped this one in and it worked first time. I
looking at the internals of the AMK regulators for 64 1/2 w/AC, the contact for the BATT terminal isn't closing. The ARM and FIELD terminals are closed by default. The terminal for the BATT is open by default (when car is off) and is supposed to close to pass the voltage to the battery. It seems that the magnet in the regulator isn't strong enough to close the contact for some reason. You can manually close the contact for Batt and it starts charging the battery. Once the car is turned off, the contact opens, so some magnetic field is working but not enough to close the contact at start up or even after running for a while with RPM run higher.
Beware the AMK voltage regulators. I'd like to find a 30 AMP NOS original for backup.