Headlight Dimmer - Automatic: Diagnosis Lincoln Mark I

PREPARATION FOR TESTING

Place car in a well-lit area. Set dimmer range control to approximate center of its range. Operate engine at fast idle to maintain constant voltage.

AUTOMATIC HEADLIGHT DIMMER SYSTEM TEST

1. Set headlight switch to ON position. Set dimmer switch to high beam position. Set dimmer sensitivity to maximum. Locate sensor at center of windshield header, behind rearview mirror. Using a paper clip, push self-test button through hole in top right of sensor.
2. Headlights should switch to low beam and back to high beam position within 5 seconds. If headlights do not switch, check circuit No. 508 (White wire between dimmer sensor and control switch) for short to ground.
3. If headlights do not return to low beam, replace sensor. If system still does not operate, continue testing.
4. Start engine, and operate it at fast idle. Set dimmer sensitivity to approximate midpoint of its travel. Headlights should remain in low beam in both positions of dimmer switch when sensor is exposed to sufficient light. If headlights do not function as specified, go to step 5). If headlights function as specified, go to step 9).
5. If headlights remain in high beam, remove high-low beam relay. High-low beam relay is located behind center of instrument panel on Continental and Mark VII and above steering column on Town Car. Connect test light between Gray/Yellow wire at relay connector and battery voltage. If test light does not glow at each position of dimmer switch, replace relay.
6. If test light glows at each position of dimmer switch, unplug dimmer switch connector. If test light continues to glow, check for short in circuit No. 505 (Gray/Yellow wire). If wire is okay, replace dimmer switch. Reconnect relay.
7. Disconnect sensor-amplifier cable at in-line connector. Connect DVOM between ground and White wire (circuit No. 508) at sensor. With dimmer range control knob fully clockwise and headlights on, meter should indicate approximately battery voltage.
8. Rotate dimmer range control knob fully counterclockwise. DVOM should indicate zero volts. Rotate knob between both positions. A smooth, continuous voltage change should occur. Replace dimmer range control if it does not operate as described in steps 7) and 8).
9. With headlights on, sensor exposed to sufficient light and dimmer switch in automatic position, disconnect sensor-amplifier cable at in-line connector. If headlights return to low beam, replace sensor-amplifier. If headlights remain on high beam, replace dimmer switch.
10. Activate flash-to-pass system by momentarily placing dimmer switch halfway between low beam and automatic positions. Headlights should switch to high beam. If headlights switch to high beam, proceed to step 11). If headlights do not switch to high beam, check for loose connection at high-low beam relay, dimmer switch connector and at in-line connector between sensor-amplifier cable and wiring harness.
11. Disconnect Red wire (circuit No. 527) from dimmer switch connector, and ground it to vehicle body. If headlights switch to high beam, replace dimmer switch. If headlights do not switch to high beam, reconnect Red wire, and check continuity of circuit through harness to dimmer range control and sensor-amplifier.
12. Set dimmer switch to automatic position. Cover sensor-amplifier lens using a black cloth. If headlights switch to high beam, remove cloth, and go to step 14). If headlights do not switch to high beam, disconnect sensor-amplifier at in-line connector.
13. Ground Gray/Yellow wire (circuit No. 505) on male connector at dimmer range control. If headlights switch to high beam, replace sensor-amplifier. If headlights do not switch to high beam, replace dimmer switch.
14. Set dimmer switch to automatic low beam. Rotate dimmer range control knob fully counterclockwise. If headlights do not switch to high beam, check dimmer range control for poor connection to ground. If headlights switch to high beam, unit is functioning properly. Check sensitivity and aiming.