In-Vehicle Testing

Remove the switch from the instrument panel but leave the switch connected, refer to ACCESSORY SWITCH BEZEL .
Turn the ignition switch ON.

Using a voltmeter, check for battery voltage at Pin 1 and 2 (Fig 1 ).

Fig 1: Identifying Rear Window Defogger Switch Harness Connector

Courtesy of DAIMLERCHRYSLER CORP.

REAR WINDOW DEFOGGER SWITCH AND HARNESS CONNECTOR PIN CALL-OUT FUNCTION

PIN	FUNCTION
1	FUSED B+
2	FUSED IGNITION SWITCH OUTPUT (RUN)
3	GROUND
4	PANEL LAMPS DRIVER
5	PANEL LAMPS DRIVER

If OK, go to Step 4.
If NOT OK, check fuse 7 in the fuse block and the 40 Amp cartridge fuse in the Power Distribution Center (PDC). If fuses are OK, check wiring circuit. Refer to appropriate Wiring Diagrams.

Check Pin 5, with switch in the ON position there should be battery voltage and no voltage in the OFF position.
1. If OK, go to Step 5.
2. If NOT OK, no voltage in the ON position or voltage in the OFF position. Replace the switch.
Press switch to ON position. The indicator lamp should come on and remain on for approximately 10 minutes. If the indicator lamp fails to light or no voltage is present for approximately 10 minutes. Replace Rear Window Defogger Switch. Refer to ACCESSORY SWITCH BEZEL .