Help Please! 1994 Tiara 31 Open Alternator/Regulator Question

[mholts13@yahoo.com]

I have Crusader 454's. The port alternator appears to be a MANDO with a internal regulator. Originally it most likely was a Prestolite 8E with a external regulator. The problem is: the Alternator is putting out 17.2 plus volts even if I just start the engine and idle. Being that I need to change the oil and put the boat away for the winter (inside heated storage) I would like to somehow disconnect the alternator so it won't charge. I can't reach the back of it to see which wires etc; so I could follow some wire to disconnect. Using the Starboard engine/alternator as a guide, I notice that there is an Isolator on the bulk head. There's a red lead going from the isolator to the D red of the alternator.  Does anyone know if I can disconnect that wire and safely be able to start that engine without doing any damage?  Any information will be much appreciated.

Thank you. 
Holts13