The alternator regulator should maintain alternator output Voltage at about 13.5 +/- ½ Volts whether the battery is there or not. Most electrical power requirements are served by the alternator, even at low speeds. The ALTERNATOR gauge on the dash should hover near the mid-point unless power windows, power seats or top motor are in use. If the battery were there and needing charging, the gauge would indicate some current in the “C” direction as some alternator current is directed to the battery through the ammeter.
If you are checking the system with the battery disconnected, I suggest monitoring the system Voltage. Actually, this Voltage should also be checked before disconnecting the battery with the engine idling. The Voltage should be stable in either case.
Most auto parts stores will perform this check with a little more sophisticated instrument for free with no obligation.
If the alternator and regulator in a 1966 300 are working as they should, could you not give it a quick and dirty test by having the engine running at a fast idle, undoing the positive cable from the battery positive post and observing..........engine quits, something is wrong. Engine keeps running.........alternator and regulator are working. Is this the way it can be tested? Ruin any diodes or other do-dads?
Larry Jett I want my children to have all the things I never could afford.............then I am moving in with them.