"GM old style"- - - - - -there were two of them, one with an extrnal regulator, and the other (10-SI) with a built-in voltage regulator. Does the 2-wire plug enter from the back of the housing or is it on the outer perimeter of the alternator?
The early model 2-wire plug is almost square, and has a semicircular indexing tab. That alternator must have an external 4-wire regulator which mounts on the firewall or the radiator support. The 10-SI alternator has a rectangular plug on its outer perimeter and one wire needs to connect to the large BAT terminal, and the other one should be connected to a switched ignition voltage source.
If you've got a 10-SI alternator, it's possible to bypass the regulator and put it into full output by inserting a shorting pin like a small-bladed screwdriver or a cotter pin into a D-shaped hole in the back of the housing near the 2-wire plug's location. This eliminates the regulator from the circuit and gives the alternator full currrent flow in the field coils. Don't run the engine above fast idle, as there will be no voltage control.
Jerry
