Im pretty sure AC used a Class A Charging System. They have one brush internally grounded BUT THE FIELD WINDINGS ARE NOTTTTTTTT internally grounded as on a Class B system like some Fords used. The one Field winding end attaches to the same point as the Armature post while its other end terminates out the gennys FLD post (isolated n insulated from case). Therefore to Polarize the genny you can momentarily flash jump a wire from the BAT terminal on the VR over to the ARM/GEN terminal. Or else direct (jump a hot ungrounded battery voltage source) to the gennys ARM post accomplishes the same thing.