How many wires on the 15.5. I know nothing about how the 11hp wiring works but the only alternators I have had anything to do with that had a/c headlight and d/c charging,this requires 2 wires for the a/c and 2 wires for the d/c. Maybe it has an a/c regulator for the headlight and a rec/reg for the d/c built inside it somewhere. Once you have the motor installed you could test the wires to see what voltage is coming out of the wires and go from there
