Hello, I went through this last spring. The auto electric guy hated me but I learned a lot about externally regulated alternators. The are three wires, on mine one is hot with the key on and fed from the fuel solenoid, one is ground and the third goes to the alternator to excite the field. An automotive shop can check it for you and tell you which spade lug on the regulator is which. If you find a shop that's been around a long time with an old guy working in it you've got it made. They will even be able to get a replacement if you need one. I'll be at my boat Thursday so I will be able to trace the wires if you need.
Walt Hoover