Things You'll Need
Instructions
Cut one 12-inch piece of red wire and two 12-inch pieces of black wire. Strip 1/2-inch of insulation off of both ends of each wire. Connect one end of the red wire to the positive terminal of the battery and connect the other end to the positive terminal of the motor. Then connect one end of the first black wire to the negative terminal of the battery and connect the other end to one of the two switch terminals.
Take the second black wire and connect one end to the motor negative terminal and connect the other end to the second switch terminal. Turn the switch to the "ON" position and the fan should run.
Turn the fan off. Clip the red volt meter probe onto the positive terminal of the battery. Touch the black probe on the negative terminal of the battery. The voltage meter should indicate full battery voltage. Now move the black probe to the switch terminal closest to the battery. That terminal should also be reading full battery voltage.
Move the black probe to the second switch terminal. That terminal should be reading zero voltage since the switch is off. if the switch was on and there was no voltage at this terminal, the switch would have to be replaced. This type of circuit can be used for an automobile cooling system by simply replacing the manual switch with a thermal switch. Thermal switches are designed to turn on when a preset temperature is reached.