I believe that the exciter wire is supposed to be wired to light bulb with the other bulb connection going to ground. It has a dual purpose of providing resistance though the exciter wire, thus "turning on" the alternator, and provide an idiot light to indicate when the charging system fails.
Wired this way, when you turn on the ignition, the idiot light (wired to the exciter wire) comes on. Once the starter turns the engine over (as well as the alternator pulley) the light goes off. The light stays off until the engine stops running (with the ignition switch still on), or when something in the charging system goes bad.
Carl
