hi- am not able to get into my '72 right now to look but you just wire it so the switch is inbetween the hot wires in your cabinet, and the motor. When you move that lever, it closes the circuit in the switch to supply
12V to the motor. I believe that one of the wires in the cabinet would go directly to the fan motor, the other would go to one of the switch terminals, and then from the other terminal to the motor. You do still have the switch, right? if not, you'll have to get one.