Test D: Auto Dimming Feature Does Not Function Properly

1. Turn ignition switch to RUN position. Move gear selector through all positions while observing reverse lights. If reverse lights only operate when gear selector is in Reverse, go to next step. If reverse lights do not operate or operate in any other position other than Reverse, repair reverse lights. See appropriate wiring diagram in BACK-UP LIGHTS article.
2. Cover light sensor on back of inside mirror. Use a flashlight to shine light into light sensor on front of inside mirror. With gear selector in Park, inside mirror should darken. With gear selector in Reverse, inside mirror should undarken. If inside mirror operates as described, system is okay at this time. If inside mirror only darkens, go to next step. If inside mirror will not undarken in Reverse, go to step  7.
3. Turn ignition off. Place gear selector in Park. Check fuse No. 23 (10-amp) in instrument panel fuse box. If fuse is okay, go to next step. If fuse is blown, replace fuse and check system for normal operation. If fuse blows again, repair short to ground in White/Light Blue wire and check system for normal operation. See WIRING DIAGRAMS .
4. Disconnect inside mirror harness connector. Turn ignition switch to RUN position. Measure voltage between ground and inside mirror harness connector terminal No. 7 (White/Light Blue wire). See Fig 1. If battery voltage does not exist, go to next step. If battery voltage exists, go to step  6.
5. Turn ignition off. Disconnect central junction box 26-pin harness connector (central junction box is located under left side of instrument panel). Measure resistance in White/Light Blue wire between inside mirror harness connector terminal No. 7 and central junction box harness connector terminal No. 1. If resistance is 5 ohms or less, replace instrument panel fuse box. If resistance is greater than 5 ohms, repair open in White/Light Blue wire and check system for normal operation. See WIRING DIAGRAMS .
6. Turn ignition off. Measure resistance between ground and inside mirror harness connector terminal No. 6 (Black wire). If resistance is 5 ohms or less, replace inside mirror assembly. If resistance is greater than 5 ohms, repair open or high resistance in Black wire and check system for normal operation. See WIRING DIAGRAMS .
7. Place gear selector in Reverse. Measure voltage between ground and inside mirror harness connector terminal No. 5 (Black/Pink wire). If battery voltage exists, replace inside mirror assembly. If battery voltage does not exist, repair open in Black/Pink wire and check system for normal operation. See WIRING DIAGRAMS .

Fig 1: Identifying Inside Mirror Harness Connector Terminals

Courtesy of FORD MOTOR CO.