Without A/C

With the ignition switch in ON or START, battery voltage is applied to the heater relay. The oil pressure switch will provide ground to the circuit once normal oil pressure is obtained. The heater relay energizes and allows battery voltage from main fuse 1 to the blower motor.

The blower switch then applies ground to the resistor block for the desired blower motor speed. As the blower switch moves from OFF to position 4, resistors in the resistor block are bypassed. This increases blower motor speed. When the fan switch is in position 4, all of the resistors are bypassed and the blower motor runs at the highest speed.