Overcharging will cause a hot battery.
The original 2 terminal regulator is a simple relay, basically a "two speed" field regulator. The alternator has one field brush grounded, and the other one connects to the output side of the regulator.
When you energize the regulator, it uses the incoming power for a voltage reference, as well as power to the field. When the car is first started, the alternator is receiving full field power. As the system voltage rises, the relay receives a high enough voltage to open the full field contacts. This leaves the field powered through a resistor in the regulator, which gives the field less power than the direct contacts, and lowers the output. This is part of what can make the ammeter needle "twitch", the relay switches suddenly when the charge voltage hits about 14.8v.
The three big causes of overcharging are bad reference voltages, failed relay windings and welded or stuck relay contacts.
The relay inside the regulator can fail. This will leave the ammeter leaning toward charge, and an overcharging condition. You will see charging voltages over 15 volts.
The contcts can stick or weld together. You can remove the cover & clean them with some 600 grit sandpaper folded in half. The symptoms are the same as a failed relay, but sometimes the contacts will unstick with a sharp rap to the regulator case with a screwdriver handle.
Reference voltages are a bit harder to track down. You need to use a decent voltmeter or DMM. With the key on, and the engine stopped, measure the voltage at the two battery posts. Now with the negative probe still on the battery terminal, measure the voltage at the regulator terminal. If the voltage is more than .35 volts lower, you have resistance in the harness circuits. Corroded wires, connectors etc. Turn the key off.
The other side of the reference voltage, is the regulator's connection to ground. The only way it can accurately sense voltage is with a good ground connection. To test this, set your DMM to resistance, or Ohms. Put one probe on the negative battery post. Noe test the resistance to the frame of the regulator - this is the metal base below the cover, or the head of a cover screw - NOT the mounting bolt or screw Should be less than 2 ohms. If it is higher than that, check the mounting bolt next.
Ground resistance on those old regulators is a big issue, and a cause of lots of trouble. A fresh coat of paint on the firewall, and a rusty washer will cause all sorts of odd voltage regulator results. Loose mounting hardware can cause erratic charging. A missing engine to body ground wire will also cause problems.
So in your case I would pull the regulator, and open it up on the bench. Clean the contacts, and re-install it with clean hardware. Clean the mounting pads on the firewall before you bolt it down too. Borrow a known good battery from another car for testing the system, no sense chasing more than one problem at a time.
The check your charging voltages, and go from there.
Hope this helps.
B.
