It sounds like you've got one of the early types of alternator that's intended to have an external regulator that's had an electronic regulator added to it. They're about 2 inches square and a half inch thick, with two wires- - - -one attached to the big charging wire terminal and the other plugged onto one of the connections in a small square hole in the back of the housing. I've installed a lot of them, and they work pretty well.
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!