When the ignition switch is on, voltage is supplied from the HVAC/DRL fuse to the rear window defogger relay and the A/C-heater control through CKT 241. The rear window defogger relay receives voltage from the REAR DEFOG fuse through CKT 1040. When the rear defogger switch is pressed, voltage is momentarily applied to the solid state timer, sending a ground signal to the rear window defogger relay through CKT 193. This energizes the rear window defogger relay. When the rear window defogger relay is energized, voltage is sent from CKT 1040 to CKT 293. This sends voltage to the rear defogger grid which is also receiving ground from G401 through CKT 450, causing the rear defogger grid to heat up. The rear window defogger relay remains energized until the defog cycle is complete or the rear defogger switch is pressed a second time.

When the ignition switch is on and the rear defogger switch is pressed for the first time, the defog cycle lasts 10 minutes. However, further operation of the rear defogger will result in 5 minute defog cycles. The defog cycle is reset to 10 minutes when the ignition switch is turned off and back to on.

The defogger ON indicator is an LED that illuminates when the rear defogger is on.