For 1990-2009 cars

Voltage is applied to the rear defogger switch, through the REAR DEFG fuse, when the ignition switch is in the ON position.

When the rear defogger switch is pressed, system voltage is applied through the closed contacts of the switch to the rear defogger indicator and to the rear defogger. The rear defogger is permanently grounded at G400. Because the rear defogger is a resistive element, the defogger begins to heat as soon as voltage is applied. The permanent grouding at G400 causes the defogger indicator to light when voltage is applied.

The rear defogger switch does not incorporate an integral timing circuit. The switch must be pressed to the OFF position in order to terminate the rear defogger operation.