Turning the ignition switch to the RUN position causes voltage to be applied through fuse 4 to the rear defogger switch in the heater-a/c control. A solid state timer controls battery voltage from fuse 4 through a relay. When the rear defogger switch is pressed, voltage is momentarily applied to the timer. This activates the relay controlling the rear window defogger grid. This relay will remain closed by the timer until the defog cycle is complete or the rear defogger switch is pressed a second time.

Turning the ignition switch to the RUN position and pressing the rear defogger switch for the first time causes the defog cycle to last 10 minutes. Further operation results in 5 minute defog cycles. The defog cycle is reset to 10 minutes when the ignition switch is turned to the OFF position and back to the RUN position.

The defogger ON indicator is a LED that illuminates when the rear defogger is ON. This LED will be step dimmed by the LED indicator control when the park lamps are turned on.