Sorry for the delayed response Cab... But just saw the question. It has been a while since i wired mine, but what I remember is most switches aren't rated to handle the voltage of the alternator going through them (?) So, the external 250 continuous duty solenoid is needed to support the alternator, and the solenoid gets wired to the switch to shut down the alternator to the battery, the switch also kills the battery feed to the rest of the car.