When you turn the ignition switch to the RUN position, voltage is supplied through fuse 4 to the rear defogger switch in the heater-A/C control. A solid state timer controls the battery voltage from fuse 4 through a relay. When you press the rear defogger switch, voltage is supplied momentarily to the timer until the defog cycle completes or until you press the rear defogger switch for a second time.

When you turn the ignition switch to RUN and press the rear defogger switch for the first time, the defog cycle lasts 10 minutes. Further operation results in 5 minute defog cycles. The defog cycle resets to 10 minutes when you turn the ignition switch to the OFF position and back to the RUN position.

The defogger ON indicator is an LED that illuminates when you turn the rear defogger ON. This LED is step dimmed by the LED indicator control when you turn the park lamps ON.

The right front filter prevents the operation of the rear window defogger from causing static during the operation of the radio.