For 1990-2009 cars

When the ignition switch is on, voltage is supplied from the HVAC/DIC/DRL/HEATED SEAT Fuse to the rear window defogger relay and the A/C-heater control through circuit 241. The rear window defogger relay receives voltage from the RR DEFOG Fuse through circuit 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 circuit 193. This energizes the rear window defogger relay closing the switch in the relay. When the rear window defogger relay is energized, voltage is sent from the RR DEFOG Fuse circuit 1040 to circuit 293. This sends voltage to the LH and RH mirrors which also receives ground from G302 through circuit 750, causing the mirrors to heat up. This also sends voltage to the rear defogger grid. For rear defogger circuit description refer to Rear Window Defogger Circuit Description . 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 and heated mirrors are on.