Hotrod, my understanding of the 3-wire, internally regulated alternator is that something had to be connected to the idiot light terminal...either an idiot light or a 10 ohm resistor supplied by an ignition source. I thought this was the terminal that provided regulator "excitation". The other plug wire is a sensor wire and is used to measure the voltage at an appropriate location, usually the "center" of the 12V distribution system. The voltage at this location will determine what voltage the alternator puts out.
