Defogger Switch Circuit Test

1. Turn ignition off. Disconnect defogger switch harness connector. Turn ignition on. Using a voltmeter, check between ground and terminal No. 4 (Blue/White wire). See Fig 1 . If battery voltage exists, go to next step. If battery voltage does not exist, check ELEC-IGN (10-amp) fuse. If fuse is okay, check for an open or short in Blue/White wire. Repair as necessary.
2. Turn ignition off. Using an ohmmeter, check for continuity between ground and terminal No. 5 (Pink/White wire). See Fig 1 . If continuity exists, go to next step. If continuity does not exist, check for an open Pink/White wire between connector and both mirror assemblies. If Pink/White wire is okay, check for faulty heating element in mirror assembly.
3. Check for continuity between ground and terminal No. 3 (Black wire). See Fig 1 . If continuity does not exist, locate and repair open in Black wire. See WIRING DIAGRAMS  .

Fig 1: Identifying Defogger Switch Harness Connector Terminals

Courtesy of ISUZU MOTOR CO.