DESCRIPTION & OPERATION
The automatic headlight dimmer switches the headlight beam from high to low in response to headlights from an oncoming vehicle or taillights from a vehicle being overtaken. The system consists of a sensor-amplifier, high-low beam relay, flash-to-pass relay, dimmer switch, dimmer range control (thumbwheel or knob operation) and indicator light.
DIMMER SWITCH
The flash-to-pass dimmer switch is located in the steering column. One switch position provides low beam operation and the other provides automatic operation. Momentarily moving dimmer switch lever half-way between positions flashes high beams. The flash-to-pass relay is identical to the high-low beam relay. Both relays are mounted under instrument panel, and use the same mounting screw.
HIGH-LOW BEAM RELAY
The high-low beam relay is a 12-volt DC unit containing heavy duty contacts for switching the headlight beams. In the low beam position, contacts are closed. The high-low beam relay also contains a diode to dampen transient electrical current that could damage the sensor-amplifier. Observe proper polarity when making connections to prevent damage to diode and, subsequently, the sensor-amplifier.
DIMMER RANGE CONTROL
The dimmer range control is the first dial to the right of the headlight switch. Its function is to adjust system sensitivity to surrounding light. Rotating the control's thumbwheel upward (or knob clockwise) toward maximum ON position increases sensitivity, and headlights dim when approaching vehicles are at a greater distance.
Rotating the dimmer range control thumbwheel downward (or knob counterclockwise) decreases sensitivity, allowing approaching vehicles to come nearer before headlights dim. Moving thumbwheel fully downward (or knob fully counterclockwise) to OFF position permits manual operation of headlight beam with column dimmer switch.
SENSOR-AMPLIFIER
The sensor-amplifier is a light sensing optical device with a transistorized amplifier to operate the high-low beam relay. The sensor-amplifier is mounted to the rearview mirror support. The unit is adjusted for aim and sensitivity at the factory; then it is completely sealed with moisture-proof epoxy. The epoxy forms a capsule and prohibits access to factory sensitivity adjustments and interior parts.
Note. If an automatic headlight dimmer malfunction cannot be immediately serviced, manual operation of headlights may be obtained at the dimmer switch by disconnecting sensor-amplifier and turning dimmer range control to the OFF position.
SENSOR-AMPLIFIER HORIZONTAL & VERTICAL AIMING
Sensor-amplifier horizontal and vertical aim is factory pre-set and not adjustable. Horizontal aiming is pre-set 2 degrees left of vertical plane.
AUTODIMMER INDICATOR INOPERATIVE
Check for burned-out bulb, and replace if necessary. Check for damaged switch in potentiometer assembly or damaged dimmer switch. To do so, turn headlights on, and place dimmer switch in automatic position. Check for battery voltage at Yellow wire of potentiometer assembly connector. (Scheme 1)-6. If battery voltage is present, replace potentiometer assembly. If no voltage is present, check dimmer switch and wiring.
NO HIGH BEAM WITH DIMMER RANGE CONTROL TURNED OFF
Check for damaged high-low beam relay, and replace if necessary. Check dimmer switch for proper operation.
NO HIGH BEAM WHEN SYSTEM IS ON AUTOMATIC
Check for loose connections or poor grounding at sensor-amplifier. Check for damaged sensor-amplifier. To do so, move dimmer range control to minimum range without turning it off. Hold a black cloth directly over sensor amplifier lens. Sensor is damaged if it does not switch to high beam within a few seconds.
HEADLIGHTS STAY IN HIGH BEAM - SYSTEM ON AUTO
Check for damaged high-low beam relay, and replace if necessary. Check for damaged sensor-amplifier. To do so, turn headlights on. Ensure sensor is exposed to sufficient light and dimmer switch is in automatic position. Disconnect sensor amplifier connector. If headlights return to low beam, replace sensor-amplifier.
HEADLIGHTS DIM TOO SOON OR TOO LATE
If headlights dim too late, clean windshield and retest. Check for loose amplifier or mirror support, and tighten as required. Check for damaged potentiometer or sensor-amplifier. See AUTOMATIC HEADLIGHT DIMMER SYSTEM TEST under TESTING & DIAGNOSIS.
NO FLASH-TO-PASS
Check for blown fuse or circuit breaker. Replace 20 amp fuse (25 amp on Town Car) in position No. 14 if necessary. Check for damaged dimmer switch. Check for damaged flash-to-pass relay. On all models except Continental, test relay to ensure Red wire (circuit No. 527) is grounded when momentarily moving dimmer switch half-way between low beam and automatic positions. (Scheme 1)-6.
NO MANUAL LOW BEAM
Check for defective high-low beam relay. To do so, remove high-low beam relay, and check for continuity between Red/Yellow wire (circuit No. 15) and Red/Black wire (circuit No. 13). Check for damaged dimmer switch. To do so, disconnect dimmer switch. See DIMMER SWITCH under REMOVAL & INSTALLATION. Replace dimmer switch if headlights return to low beam. Check for damaged flash-to-pass relay. To do so, remove relay. Replace relay if headlights return to low beam.
PREPARATION FOR TESTING
Automatic headlight dimmer is a transistorized system and needs no warm-up. Place car in a well-lighted area, and adjust dimmer range control to approximate center of its rotation. Operate engine at fast idle to maintain constant voltage.
Scheme 1
Scheme 2
AUTOMATIC HEADLIGHT DIMMER SYSTEM TEST
- Turn headlight switch to ON position. Expose sensor to sufficient light. Headlights should remain in low beam position for both positions of dimmer switch. If headlights remain on low beam in both positions of dimmer switch, proceed to step 7).
- If headlights remain in high beam position for both positions of dimmer switch, remove high-low beam relay from its connector. See HIGH-LOW BEAM & FLASH-TO-PASS RELAYS under REMOVAL & INSTALLATION. Connect one lead of test light to battery voltage and other lead to Yellow/Gray wire of relay connector. (Scheme 4)-6. If test light does not light for both positions of dimmer switch, replace relay.
- If test light lights, remove dimmer switch connector. If test light remains lit, check for short in circuit No. 505. If no short, replace dimmer switch, and reconnect relay.
- Disconnect sensor-amplifier cable at in-line connector. Connect voltmeter between ground and White wire (circuit No. 508) at sensor. With dimmer range control thumbwheel fully upward (knob fully clockwise) and headlights on, meter should read approximate battery voltage.
- Rotate dimmer range control thumbwheel fully downward (knob fully counterclockwise). Meter should read zero volts. Rotate thumb-wheel between both positions. A smooth, continuous voltage change should be indicated. Replace dimmer range control if it does not operate as described in steps 4) and 5).
- 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.
- Activate flash-to-pass system by momentarily moving dimmer switch half-way between low beam and automatic positions. Headlights should switch to high beam. If headlights switch to high beam, proceed to step 9). 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.
- Also 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.
- Move dimmer switch to automatic position, and cover sensor-amplifier lens with a black cloth. Headlights should switch to high beam. Remove cloth and proceed to step 11). If headlights do not switch to high beam, disconnect sensor-amplifier at in-line connector.
- Ground Gray/Yellow dot 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.
- Place headlights on automatic low beam, and rotate dimmer range control's thumbwheel fully downward (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, proceed to next step.
- If system responds correctly to all tests, unit is functioning properly. Check sensitivity and aiming.
Continental, Cougar, Mark VII & Thunderbird
- Connect an ohmmeter to terminals No. 1 and 4 on back of potentiometer (terminals No. 1 and 2 on Mark VII). (Scheme 1)and (Scheme 2). With dimmer range control in OFF position, ohmmeter should read 8000-12,000 ohms. Rotate dimmer range control to maximum ON position. Ohmmeter should read 2800-4600 ohms.
- Connect ohmmeter to terminals No. 3 and 8 (terminals No. 3 and 6 on Mark VII). Continuity should exist only with dimmer range control in OFF position.
- Connect ohmmeter to terminals No. 4 and 8 (terminals No. 2 and 6 on Mark VII). With dimmer range control in OFF position, ohmmeter should read 8000-12,000 ohms. With dimmer range control in other positions, ohmmeter should read about 100 ohms. If ohmmeter reads more than 8000-12,000 ohms, replace indicator bulb.
Town Car
Use self-powered test light or ohmmeter to check continuity in appropriate switch positions. See HEADLIGHT SWITCH POSITION TEST (TOWN CAR) table. (Scheme 3)
| Terminals | Off | Park | On |
|---|---|---|---|
| B to H | No Cont. | No Cont. | Continuity |
| B to R | No Cont. | No Cont. | No Cont. |
| B to A | No Cont. | No Cont. | No Cont. |
| R to H | No Cont. | No Cont. | No Cont. |
| R to A | No Cont. | Continuity | Continuity |
| H to A | No Cont. | No Cont. | No Cont. |
| C to Ground | No Cont. | Continuity | Continuity |
| E to B | Continuity | Continuity | Continuity |
| C to B | No Cont. | No Cont. | No Cont. |
| D1 to D2 | (1) | (1) | (1) |
| I to R | (2) | (2) | (2) |
| (1) Continuity should only exist with rheostat in full clockwise position. (2) Continuity should exist with rheostat in full counterclockwise position (test light should glow brightly). Slowly rotate rheostat clockwise and test light should slowly dim. | |||
| (1) | Continuity should only exist with rheostat in full clockwise position. |
| (2) | Continuity should exist with rheostat in full counterclockwise position (test light should glow brightly). Slowly rotate rheostat clockwise and test light should slowly dim. |
HEADLIGHT SWITCH POSITION TEST
Scheme 3
Removal & Installation
Disconnect battery ground cable. Remove steering column trim shroud. Disconnect dimmer switch lever by pulling lever from switch with a twisting motion. Remove foam backing from switch. Remove connectors and screws. Remove switch. To install, reverse removal procedure.
Disconnect battery ground cable. Remove pad below steering column. Remove lower cluster lens and left side finish molding. Remove lower left side pad. Remove relay from instrument panel brace, and disconnect relay from connector. To install, reverse removal procedure.
Disconnect plug at rear of unit. Remove mounting screw, and remove unit from mirror support. To install, position sensor-amplifier on support and tighten screw. Ensure mirror support is tight.
WIRING DIAGRAMS
Note. Mark VII headlight dimmer wiring schematic is not available from manufacturer.
For additional information, see appropriate chassis wiring diagram in WIRING DIAGRAMS.
