Electric Window Defoggers: Operation

A relay timer and switch provide automatic control of system. Switch positions are "ON", "OFF" and "NORM". The "ON" and "OFF" positions are spring loaded and return to "NORM" when released. An indicator light will glow when system is operating. When unit is turned on, current flows through timer to system's alternator field; alternator then transmits about 120 volts to front and rear glass. The timer limits high voltage current to glass for about ten minutes; then automatically cuts output to low voltage. This is accomplished by a 2.2 ohm resistor being inserted in field current by a timer. The engine must be operated at 1500 RPM for alternator to deliver high voltage. See Motorcraft High Voltage Alternator in ELECTRICAL Section.