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Control Assembly Test: Probe

  1. Set ignition switch to ON position. Turn on and check rear window defogger. If rear window defogger is not working at all, go to next step. If rear window defogger is operating only in some places, go to step 14).
  2. Ensure rear window defogger indicator light is on. If indicator light is not on, go to next step. If indicator light is on, go to step 6).
  3. Ensure fuse is in good condition. If fuse is okay, go to step 4). If fuse is blown, check for shorts to ground in Black/Yellow wire at rear window defogger switch, and repair as necessary. Replace fuse.
  4. Ground Black wire at rear window defogger switch. If indicator light comes on, repair Black wire between rear window defogger switch and ground. If indicator light does not come on, go to next step.
  5. Check for battery voltage on Black/Yellow wire at rear window defogger switch connector. See Fig 1 . If battery voltage is present, replace switch. If battery voltage is not present, repair Black/Yellow wire between switch and fuse panel.
    Fig 1: Locating Control Assembly Test Points (Probe)
    G91F11788Courtesy of FORD MOTOR CO.
  6. Check for battery voltage on Black/Blue wire at rear window defogger relay, located on relay module under left side of instrument panel. If battery voltage is not present, go to next step. If battery voltage is present, go to step 12).
  7. Check rear window defogger circuit breaker. If circuit breaker is tripped, reset circuit breaker. If circuit breaker trips again, check for short to ground in Black/White wire. Repair Black/White wire as necessary, and reset circuit breaker. If circuit breaker is not tripped, go to next step.
  8. Remove defogger relay. Check for battery voltage on Black/White wire at relay connector. If battery voltage is present, go to next step. If battery voltage is not present, repair Black/White wire between rear window defogger relay and fuse panel.
  9. Check for battery voltage on Black/Yellow wire at rear window defogger relay connector. If battery voltage is present, go to next step. If battery voltage is not present, repair Black/Yellow wire between rear window defogger relay and fuse panel.
  10. Turn ignition off. Connect a jumper wire between Black/White wire on relay connector and corresponding terminal on relay. Connect a jumper wire between Black/Yellow wire on relay connector and corresponding terminal on relay. Turn ignition on. Ground Black/Blue wire at rear window relay.
  11. Check for battery voltage on Black/Blue wire at rear window defogger relay. If battery voltage is present, repair Black/Blue wire between rear window defogger relay and rear window defogger switch. If battery voltage is not present, replace rear window defogger relay.
  12. Check for battery voltage on Black/Blue wire at rear window defogger connector. If battery voltage is present, go to next step. If battery voltage is not present, repair Black/Blue (10-gauge) wire between rear window defogger relay and rear window defogger.
  13. Check for continuity in Black wire between rear window defogger connector and ground. If continuity does not exist, repair Black wire between rear window defogger and ground. If continuity exists, repair or replace rear window.
  14. Set rear window defogger switch to ON position. Using voltmeter, check center of each filament. If voltmeter indicates approximately 6 volts, filament is okay. If voltmeter indicates zero or 12 volts, replace or repair filament as necessary.
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