DESCRIPTION & OPERATION
The automatic headlight dimmer is a driver-operated device which automatically switches headlights from high to low beam in response to headlights from oncoming vehicles or tail lights from a vehicle being overtaken. Major components of the system are as follows
SENSOR AMPLIFIER
Unit is located behind grille on driver's side of vehicle (Town Car only) and on rear view mirror support on all others. Unit combines a light-sensing optical device and transistorized amplifier in one unit. Sensitivity is adjusted at the factory and unit is sealed in epoxy to prevent further adjustment.
POWER RELAY
Provides heavy duty contacts for switching headlight beams. Relay contains diode (on all but Town Car) for damping purposes to protect sensor amplifier. Observe proper polarity when connecting relay to prevent diode damage.
Continental, Cougar, Mark VII & Thunderbird
Dimmer range control is the first dial to the right of headlight switch. Rotating dial up toward "MAX" increases sensitivity and headlights will switch when vehicles are farther away. Downward decreases sensitivity, allowing approaching vehicles to come nearer before headlights dim. Moving the dial fully downward to the "OFF" position permits manual operation of headlight beams with column dimmer switch.
Town Car
Driver sensitivity control is large bezel on the headlight switch. Rotating it clockwise increases sensitivity and headlights will switch when vehicles are farther away. Counterclockwise rotation decreases sensitivity, allowing approaching vehicles to come nearer before headlights dim. Full counterclockwise position permits manual operation of headlight beams with column dimmer switch.
DIMMER SWITCH
The dimmer switch used is a special flash-to-pass type (Mark VII, Continental, Thunderbird and Cougar) or over-ride type (Town Car) located in the steering column. One position provides low beam operation; the other is automatic operation. Moving the lever half-way between positions allows the driver to flash the high beams.
SENSOR-AMPLIFIER VERTICAL AIMING
Sensor-Amplifier horizontal and vertical aim is factory pre-set and not adjustable. Horizontal aiming is pre-set slightly to the left (2°) of horizontal plane. When replacing a Sensor-Amplifier be certain to use Green label for Continental and Orange label for all others.
HEADLIGHTS STAY ON LOW
Defective sensor amplifier. Defective relay or dimmer switch. Wiring problem.
HEADLIGHTS STAY ON HIGH BEAM
Defective sensor amplifier. Damaged high-low beam relay.
HEADLIGHTS DIM TOO SOON OR TOO LATE
Driver control adjustment. Dirty sensor lens, chamber or windshield. Loose amplifier or support. Defective sensor amplifier. Damaged potentiometer.
NO FLASH-TO-PASS
Defective dimmer switch, relay or wiring. Blown fuse in fuse block.
NO MANUAL LOW BEAM
Defective power relay. Defective dimmer switch or wiring. Defective flash-to-pass relay.
PREPARATION FOR TESTS
The transistorized unit needs no warm-up time. Place car in a lighted area, adjust sensitivity control to a central position, and operate engine at a fast idle to maintain constant voltage.
- Turn headlight switch on. Headlights should remain on low beam in both positions of the dimmer switch. If so, go to step 7). If not, proceed as follows
- Remove power relay. Connect one lead of test lamp to battery voltage and other lead to Violet wire of the relay connector. If test lamp does not light for both positions of dimmer switch, replace the relay.
- If test lamp does light, remove dimmer switch connector. If lamp remains lighted, repair short in circuit. If not, replace dimmer switch and reconnect relay.
- Disconnect sensor-amplifier cable at in-line connector. Connect voltmeter between ground and White wire at sensor. With sensitivity control fully clockwise and headlights on, meter should read battery voltage.
- Rotate control fully counterclockwise. Meter should read 0 volts. Rotate control between the two positions. A smooth, continuous voltage change should be indicated. If control does not operate as described in steps 4) and 5), replace sensitivity control.
- 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 not, replace dimmer switch.
- Pull part way up on dimmer switch to activate flash-to-pass system. Headlights should switch to high beam. If so, go to step 9). If not, check for loose connection at power relay, dimmer switch connector near driver sensitivity control, or in-line connector between sensor-amplifier cable and wiring harness.
- Disconnect Red wire from dimmer switch and ground to vehicle body. If headlights switch to high beam, replace dimmer. If not, reconnect wire and check continuity of circuit through harness to sensitivity control and sensor-amplifier.
- Place dimmer switch in "AUTOMATIC" position and tightly cover sensor-amplifier lens with a black cloth. Headlights should switch to high beam. If so, remove cloth and go to step 11). If not, disconnect sensor-amplifier at in-line connector.
- Ground Gray/Yellow Dot wire on engine compartment wiring harness connector. If headlights switch to high beam, replace sensor-amplifier. If not, replace dimmer switch.
- Place headlights on automatic low beam and rotate sensitivity control fully counterclockwise. Headlights should switch to high beam. If so, go to step 12). If not, check sensitivity control for poor connection to ground.
- If the system responded correctly to all the tests, the unit is functioning properly and only sensitivity and aiming remain to be checked.
All Other Models
- Connect an ohmmeter to terminals 1 and 2 on back of potentiometer. With dial in "OFF" position, ohmmeter should read 8000-12,000 ohms. Move dial to "MAX" position. Ohmmeter should read 2800-4600 ohms.
- Connect ohmmeter to terminals 3 and 6. There should be continuity with dial in "OFF" position and no continuity in any other position.
- Connect ohmmeter to terminals 2 and 6. With dial in "OFF" position, ohmmeter should read 8000-12,000 ohms. With dial in any other position, ohmmeter should read about 100 ohms. If not, replace indicator bulb. (Scheme 4)
Continental, Cougar, Mark VII & Thunderbird Potentiometer Test Locations. Scheme 4
Removal & Installation
Disconnect battery ground cable. Remove steering column shroud and disconnect dimmer switch lever by pulling out of switch with a twisting motion. Peel back foam from switch, remove connectors and screws and remove switch. To install, reverse removal procedure.
Removal & Installation (Town Car)
Disconnect battery ground cable. Remove attaching screw securing relay to left fender reinforcement. Disconnect connector from relay. To install, reverse removal procedure.
Removal & Installation (All Other Models)
Disconnect battery cable. Remove pad below steering column. Remove lower cluster lens left side finish moulding. Remove lower left side pad. Remove relay from instrument panel brace and disconnect relay from connector. To install, reverse removal procedure.
Disconnect battery ground cable and wiring harness at rear of sensor assembly. Remove screws and lockwashers, and remove sensor amplifier from vehicle. Ensure sensor lens is clean. To install, reverse removal procedure.
Disconnect plug at rear of unit. Remove mounting screw and remove unit. To install, be certain mirror support is tight. Position sensor amplifier on support and tighten screw. Install electrical connections.
