HEADLIGHTS STAY ON IN DAYLIGHT INSPECT TWILIGHT PHOTOCELL. Cadillac Commercial Limo/Hearse Chassis 1991

For 1990-2009 cars

# HEADLIGHTS STAY ON IN DAYLIGHT INSPECT TWILIGHT PHOTOCELL

#### SUBJECT: HEADLIGHTS REMAIN ON IN DAYLIGHT (ADJUST PHOTOCELL/REPLACE PHOTOCELL/REPLACE TWILIGHT SENTINEL AMPLIFIER MODULE)

VEHICLES AFFECTED: 1991 'C'

Some 1991 DeVilles and Fleetwoods built prior to VIN breakpoint 252931 may experience headlights remaining on in daylight conditions when the twilight sentinel switch is on. This condition may be caused by improper assembly of the twilight sentinel photocell. The photocell bracket may be rotated on its screw allowing the photocell to be partially covered by the instrument panel upper trim pad. This will cause the photocell to detect darkness at all times.

To repair this condition use the following procedure:

1. Remove the instrument panel upper trim pad, refer to Section 8C in the Service Information Manual.

2. Loosen the screw retaining the bracket to the instrument panel.

3. Rotate the bracket so that the flat end rests in the U-shaped notch in the bracket retainer. Refer to Figure 1.

4. Tighten screw and replace instrument panel upper trim pad.

If, after adjusting the photocell, the headlights remain on in early daylight hours or before dusk, verify the operation of the photocell. Measure the resistance while the photocell is shielded from light and while shining a bright light (a flashlight is preferred) on it. The resistance should be less than 35 K in bright light and greater than 95 K in dark conditions. If the photocell is not operating correctly, replace it with P/N 914032.

Check photocell circuits 278 (white wire) and 803 (black/white wire) for opens. Also, check circuit 10 (yellow wire) from the twilight sentinel module pin F and light switch pin B to the headlight dimmer switch for a short to voltage.

Verify that the resistance to ground on twilight sentinel amplifier ground circuit 803 (black/white wire) is less than 1 ohm.

If the photocell and associated wiring operates correctly, the cause may be the twilight module; replace the twilight sentinel amplifier module, P/N 16515789.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.