Test D: Auto Dimming Feature Malfunction

1. Ensure parking brake is applied. Turn ignition switch to RUN position. Place gear selector in Reverse. If reverse lights operate, go to next step. If reverse lights do not operate, repair reverse lights as necessary. See BACK-UP LIGHTS article.
2. Turn ignition switch to LOCK position. Disconnect inside rear view mirror 7-pin harness connector C900. Turn ignition switch to RUN position. Measure voltage between ground and inside rear view mirror harness connector C900 terminal No. 7 (Violet/Orange wire). See Fig 1 . If more than 10 volts exists, go to next step. If 10 volts or less exists, repair open in Violet/Orange wire.
3. Turn ignition switch to LOCK position. Measure resistance between ground and inside mirror harness connector C900 terminal No. 6 (Black wire). If resistance is 5 ohms or less, go to next step. If resistance is greater than 5 ohms, repair open or high resistance in Black wire.
4. Turn ignition switch to RUN position. Place gear selector in Reverse. Measure voltage between ground and inside mirror harness connector C900 terminal No. 5 (Black/Pink wire). Battery voltage should exist when transmission is in Reverse and battery voltage should not exist with transmission in any other gear. If voltage is as specified, replace inside rear view mirror. If voltage is not as specified, repair open in Black/Pink wire.

Fig 1: Identifying Inside Mirror Harness Connector C900 Terminals

Courtesy of FORD MOTOR CO.