Starting at G200, ground travels up to normally-open momentary contacts inside the Rear Defogger Switch. Briefly closing the contacts initiates the timer in the Defogger relay
which closes its internal switch for a predetermined length of time. The switch feeds 12 volts to splice S257 causing three actions take place simultaneously: one, the PCM
sends a signal to the Idle Air Control (IAC) to up the idle speed in anticipation of the additional electrical load on the alternator which in turn puts an additional mechanical load
on the engine, two, the defogger switch in the dash lights up and three, the heating element on the rear window starts getting warm.