Test D: Rear Defogger Switch On Indicator Inoperative

WARNING: This page is about a different car, the 2002 Mercury Grand Marquis and 2002 Ford Crown Victoria. However, it is still accessible from the selected car via links, so may be relevant.

NOTE: Perform all voltage and resistance tests using a Digital Volt-Ohm Meter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in test procedure. Use ohmmeter to isolate wiring harness shorts or opens.

Turn ignition switch to RUN position. Press rear window defogger switch to ON position. If rear window defogger operates correctly, go to next step. If rear window defogger does not operate correctly, perform TEST B: REAR WINDOW DEFOGGER INOPERATIVE .
Turn ignition switch to LOCK position. Disconnect rear window defogger switch 7-pin harness connector C241, located behind top center of dash panel. See Figure. Turn ignition switch to RUN position. Using WDS or NGS tester, access Lighting Control Module (LCM) active command HEATED BACKLIGHT. Measure voltage between ground and rear window defogger switch harness connector C241 terminal No. 4 (Dark Green/Violet wire). See Figure. See WIRING DIAGRAMS . Trigger RLY CNTRL ON. If voltage is 10 volts or less, go to next step. If voltage is greater than 10 volts, replace rear window defogger switch. After repair, test system for normal operation.
Turn ignition switch to LOCK position. Remove and inspect fuse No. 10 (10-amp) from Central Junction Box (CJB), located behind left side of instrument panel. See Figure. See WIRING DIAGRAMS . If fuse No. 10 is faulty, go to next step. If fuse No. 10 is okay, repair open circuit in Dark Green/Violet wire between rear window defogger switch and CJB. After repair, system for normal operation.
Ensure ignition switch is in LOCK position. Measure resistance between ground and rear window defogger switch harness connector C241 terminal No. 4 (Dark Green/Violet wire). See Figure. See WIRING DIAGRAMS . If resistance is greater than 10 k/ohms, replace rear window defogger switch. If resistance is 10 k/ohms or less, repair short to ground in Dark Green/Violet wire between rear window defogger switch and CJB. After repair, clear DTC and test system for normal operation.