Usually, the housing will be stamped "F" and "A" (field and armature). If not, look inside the housing. The Armature (charging output) post will be wired to one of the brushes, and the Field terminal will be attached to a small diameter solid wire going to one of the Field coils in the housing. It's not impossible for a rebuilder to attach the wires backwards during an overhaul of the generator.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!