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Test B: Rear Window Defogger Does Not Turn Off Automatically

WARNING: This page is about a different car, the 2002 Ford Mustang. 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.
  1. Turn ignition switch to LOCK position. Disconnect 5-pin rear window defogger relay harness connector C2021. See Figure. Rear window defogger relay is located behind center of instrument panel. See Figure. Turn ignition switch to RUN position. Depress rear window defogger button OFF. Measure resistance between ground and rear window defogger relay harness connector C2021 terminal No. 85 (Yellow/Black wire). If resistance is 10 k/ohms or less, go to next step. If resistance is more than 10 k/ohms, go to step  3.
  2. With ignition switch on LOCK position. Disconnect 12-pin instrument cluster harness connector C220a. See Figure. It may be necessary to remove instrument cluster for access to connector. See INSTRUMENT CLUSTER  under REMOVAL & INSTALLATION. Measure resistance between ground and instrument cluster harness connector C220a terminal No. 10 (Yellow/Black wire). If resistance is more than 10 k/ohms, go to step  4. If resistance is 10 k/ohms or less, repair short circuit to ground in Yellow/Black wire between instrument cluster and rear window defogger relay. For REAR WINDOW DEFOGGERS circuit identification, see WIRING DIAGRAMS . After repair, test system for normal operation.
  3. With ignition switch on LOCK position. Disconnect rear window defogger grid harness connector C402a. See Figure. Located on left side of rear window defogger grid. See Figure. Turn ignition switch to RUN position. Measure voltage between ground and rear window defogger grid harness connector C402a (Brown/Light Blue wire) terminal. If 10 volts or less exist, replace rear window defogger relay. If more than 10 volts exist, repair short circuit to battery voltage in Brown/Light Blue wire between rear window defogger relay and rear window defogger grid. For REAR WINDOW DEFOGGERS circuit identification, see WIRING DIAGRAMS . After repair, test system for normal operation.
  4. Turn ignition switch to LOCK position. Disconnect all instrument cluster harness connectors. Inspect all instrument cluster harness connectors for loose, damaged or corroded terminals. If terminals are damaged, repair or replace as necessary. If terminals are not damaged, reconnect all instrument cluster harness connectors. Ensure instrument cluster harness connectors are seated properly. If problem still exists, replace instrument cluster. See INSTRUMENT CLUSTER  under REMOVAL & INSTALLATION. After repair, test system for normal operation.
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