Test I: Auto Dimming Does Not Operate Properly
- Turn ignition switch to RUN position. Move shift control selector through all positions. If reverse lights illuminate only while shift control selector is in Reverse, go to next step. If reverse lights illuminate in any gear position other than Reverse or not at all, repair reverse lights as necessary. See EXTERIOR LIGHTS in appropriate SYSTEM WIRING DIAGRAMS article in ELECTRICAL.
- Move shift control selector to Park. Using dark tape, cover sensor on rear of mirror (windshield side). Using a flashlight, direct light into interior rear view mirror front sensor (reflective side). Mirror should darken. Move gear shift selector to Reverse. Mirror should lighten. If mirror operates as specified, auto dimming is operating properly at this time. If mirror does not darken, go to next step. If mirror does not lighten when shifted into Reverse, go to step 7.
- Turn ignition switch to LOCK position. Move shift control selector to Park. Remove and check central junction box fuse No. 23 (10-amp). If fuse is okay, go to next step. If fuse is open, replace fuse. Recheck system operation. If fuse opens again, repair short to ground in White/Light Blue wire between central junction box and interior rear view mirror. See WIRING DIAGRAMS . Recheck system operation.
- Disconnect interior rear view mirror 7-pin harness connector C904. Turn ignition switch to RUN position. Measure voltage between ground and interior rear view mirror harness connector C904 terminal No. 7 (White/Light Blue wire). See Fig 1. If 10 volts or less exists, go to next step. If more than 10 volts exists, go to step 6.
- Turn ignition switch to LOCK position. Disconnect central junction box 34-pin harness connector C243. Central junction box is located under left side of instrument panel. Measure resistance in White/Light Blue wire between interior rear view mirror harness connector C904 terminal No. 7 and central junction box harness connector C243 terminal No. 1. See Fig 1 and Fig 2
. If resistance is 5 ohms or less, replace central junction box. See CENTRAL JUNCTION BOX under REMOVAL & INSTALLATION. Recheck system operation. If resistance is more than 5 ohms, repair open in White/Light Blue wire between interior rear view mirror and central junction box. See WIRING DIAGRAMS . Recheck system operation.
- Turn ignition switch to LOCK position. Measure resistance between ground and interior rear view mirror harness connector C904 terminal No. 6 (Black wire). See Fig 1. If resistance is 5 ohms or less, replace interior rear view mirror. See INTERIOR REAR VIEW MIRROR under REMOVAL & INSTALLATION. Recheck system operation. If resistance is more than 5 ohms, repair open in Black wire between interior rear view mirror and ground. Ground point is located near fuel tank.
- Disconnect interior rear view mirror 7-pin harness connector C904. Move shift selector to Reverse. Measure voltage between ground and interior rear view mirror harness connector C904 terminal No. 5 (Black/Pink wire). See Fig 1. If more than 10 volts exists, replace interior rear view mirror. See INTERIOR REAR VIEW MIRROR under REMOVAL & INSTALLATION. Recheck system operation. If 10 volts or less exists, repair open in Black/Pink wire between digital transmission range sensor and interior rear view mirror. See WIRING DIAGRAMS . Recheck system operation.
Courtesy of FORD MOTOR CO.
Courtesy of FORD MOTOR CO.