Circuit Operation

CIRCUIT OPERATION
The rear window defogger system is powered by circuit A4 from fuse 12 in the Power Distribution Center (PDC). Circuit A4 is HOT at all times.

In the RUN position, the ignition switch connects circuit A2 from fuse 3 in the PDC with circuit A22. Circuit A22 connects to the fuse block bus bar that powers circuit F20 through fuse 6. Circuit F20 supplies battery voltage for the timer circuitry inside the rear window defogger switch. Circuit Z1 provides ground for timer circuitry.

When the operator presses the rear window defogger switch, contacts internal to the switch close to start the timer. Circuit A4 also connects to circuit C15 at this time. When the switch is released, the timer circuitry keeps the relay energized for the specified time.

Current flows to the rear window defogger grid from the switch on circuit C15. The grid consists of two bus bars and grid lines that form a parallel circuit. When current flows through the grid, the grid lines heat up and transfer the heat to the rear window.

Circuit Z1 supplies ground for the rear window defogger grid.

When the system is in operation, a Light Emitting Diode (LED) located in the switch, indicates to the operator that the system is functioning. Also, when the headlamp switch is in the PARK or ON position, circuit E2 supplies battery voltage to the illumination lamp. When the headlamp switch is in the ON or PARK position, circuit E1 supplies voltage to circuit E2 through fuse 20 in the fuse block.