GM Service Manual Online
For 1990-2009 cars only

Exterior Lamps

The exterior lighting system consists of the following lamps:

    • The headlamps
    • The daytime running lamps (DRL)
    • The front park/turn signal lamps
    • The hazard lamps
    • The tail lamps
    • The stop lamps and center high-mounted stop lamp
    • The backup lamps
    • The license plate lamps

Headlamps

The turn signal/headlamp switch lever is located on the left side of the steering column. A twist-type knob on the end of the switch lever controls the operation of the parking lamps and headlamps. A solid tone will sound as a reminder if you open the drivers door with the key out of the ignition and the park lamps or the headlamps on. When either the parking lamps or headlamps are activated, the following lamps also illuminate:

    • The tail lamps
    • The rear license plate lamps
    • The instrument cluster assembly lamps
    • The cigar lighter lamp
    • The I/P ashtray lamp
    • The manual selector lever lamp

Voltage is applied continuously to the HLP relay pins 2 and 4 through the 30 A H MAIN fuse. The coil is energized when the daytime running lamps control module is active in normal park or headlamp operation. When the coils are energized current flows through the HLP R and HLP L fuses and then into the lamps mentioned above.

The instrument panel and instrument cluster assembly illumination lamps intensity is controlled by the I/P lamp dimmer, instead of remaining at 100 percent.

Low Beam System Operation

The headlamps may be turned on two different ways. First, when the end of the of the turn signal/headlamp switch lever is turned to the second detent position, the headlamps will illuminate. A ground signal is provided to the DRL control module. The module then provides a ground path to the coils of the HLP relay. Since the head relay is provided with battery voltage to both the contacts and the coil, the coil becomes energized and closes the contacts providing voltage to the DIM relay. With voltage and ground provided, the low beam lamps light. Second, with the switch in the OFF position, for automatic lamp control (ALC). During ALC the headlamps will be in one of the following modes of operation:

    • Daytime running lamp (DRL) operation in daylight conditions, refer to DRL below for the operation of the circuit.
    • Low beam headlamp operation in low light conditions. When the ambient light sensor senses a low light condition for approximately 15 seconds, it will cancel DRL operation and turn on the headlamps at 100 percent intensity. A path to ground is provided to the coil of the HLP relay. With a direct path to ground provided to the headlamps though the DRL control module, the headlamps will light at 100 percent intensity.

High Beam System Operation

The high-beam headlamp operation is controlled using the turn signal/headlamp switch lever on the steering column. In order to change headlamp operation from low-beam to high-beam, push the switch lever toward the instrument panel (until the detent is felt) and release. With the switch lever in the high beam position, ground is provided to the DRL control module through the turn signal/headlamp switch and splice pack 200 to G200. The DRL control module provides a ground to the coil of the dimmer relay. Since voltage is being applied to the dimmer relay coil, it becomes energized. Voltage is then applied through the closed contacts of the dimmer relay and the to the high beam lamps in the headlamps. Since ground is provided to the headlamps through the closed contacts of the energized DIM relay, the high beam lamps light. The high-beam indicator (blue) in the instrument cluster will light during high-beam headlamp operation. In order to change headlamp operation back to low-beam operation, pull the turn signal switch lever toward the driver (until the detent is felt) and release.

Flash-to-Pass System Operation

The Flash-to-Pass feature allows the driver to signal the driver of another vehicle his intention to pass. This is achieved by pulling the lever toward the driver, which will cause the high beam operation to illuminate until the lever is released. The operation of the headlamps with the turn signal/headlamp switch in flash-to-pass mode is the same as the operation of the switch in the high beam mode except the lamps will turn off when the switch is released.

Refer to Headlamp Switch Replacement for turn signal/headlamp switch removal and installation procedures.

Daytime Running Lamps (DRL)

Daytime running lamps (DRL) are standard equipment on all models. With the ignition switch in START, voltage is applied to the DRL control module through the gauge fuse. Operating through the low beams at 80 percent intensity of the normal output, a number of conditions must be met before the daytime running lamps system will work properly:

    • The engine is running.
    • The light switch is in either the OFF or the PARK lamp position.
    • The ambient light sensor senses a bright light condition.
    • The park brake is not applied.

When the above conditions are met, a path to ground is provided to the coil of the head relay. Voltage is applied through the closed contacts of the head relay, through the dimmer relay and the head fuses (L HLP and R HLP) to the low beam lamps in the headlamps. A path to ground is then provided through the DRL control module which reduces the intensity of the headlamps to 80 percent.

The following will prevent DRL operation:

    • When the generator is not running, a switch in the generator closes, providing a ground to the DRL control module, disabling the DRL operation.
    • When the light switch is in the head position.
    • When the park brake is applied.

Front Park/Turn Signal Lamps

Mechanical System Operation

The front park/turn signal lamps are located next to the headlamp assembly. The turn signal/headlamp switch lever is located on the left side of the steering column. Turn the end of the switch lever to the first detent position in order to turn on the park lamps. When a turn is signaled, the appropriate front park lamp flashes to signal a turn. The turn signals operate only with the ignition switch in the ON or START positions and will not operate during hazard flasher operation. When making a partial turn, such as when changing lanes, the driver has the option of moving the lever to a detent stop. The turn signal lamps and the turn signal indicator will continue to flash as long as the lever is held in this position and will cancel automatically when the lever is released. The detent position allows a lane change or shallow turn to be made without failing to cancel the turn signal lamp. Moving the lever past the detent position to its furthest upward or downward position will provide conventional turn signal operation. Turn signal operation is controlled by the turn/hazard signal relay located in Junction Block #1 and the turn signal/headlamp switch lever. The park/turn signal lamp lens is clear over the park lamp and amber over the turn signal lamp. It contains one amber double filament bulb.

Circuit Operation

Voltage is applied from the GAUGE fuse to cavity 1 of the flasher relay. When the contacts on the Turn switch are closed it applies a ground to the flasher relay. Current flows only to the left or right set of lamps from the flasher relay , depending which way the turn signal switch is turned to.

The following lamps are turned on pertaining to the side the switch is activated to:

    • The left or right front turn lamp
    • The left or right rear turn lamp
    • The left or right indicator lamp

Hazard Lamps

Mechanical System Operation

The hazard switch is located above the heater control assembly and controls the operation of the hazard lamp circuit. Pressing the hazard switch to the ON position will cause the turn/hazard signal relay to disengage the turn signal circuit and engage the hazard lamp circuit. This causes both turn indicators in the instrument cluster assembly to flash on and off along with all exterior turn signal lamps. The hazard lamp circuit will operate regardless of the position of the ignition switch. Press the hazard switch a second time in order to turn the hazard lamps off. Turning the hazard switch off disengages the hazard lamp circuit and returns the turn/hazard signal relay to the turn signal mode.

Refer to Hazard Warning Switch Replacement for hazard switch removal and installation procedures.

Circuit Operation

Voltage is applied from Gage fuse to the flasher relay. When turned to the on position ground is provided to Cavity 8 of the flasher relay. Current is then provided to the flashers turning them on. The hazard lamps are individually grounded.

The following lamps are turned on when the hazard switch is switched to the ON position:

    • The left and right front turn lamp
    • The left and right rear turn lamp
    • The left and right indicator lamp

Tail Lamps

The tail lamps are located on the vehicle body at each side of the rear tailgate. Each tail lamp consists of the following single filament bulbs:

    • The side marker bulb
    • The backup bulb
    • The turn signal bulb

The tail lamp lens is multi colored. A red lens covers the stop lamp and the side marker lamp, an amber lens covers the turn signal lamp and a clear lens covers the backup lamp.

Stop Lamps and Center High-Mounted Stop Lamp

Mechanical System Operation

Each of the tail lamps also contains a double filament stop lamp bulb. The stop lamp filament lights under the following conditions:

    • The stop lamp switch is closed.
    • The parking lamps are activated.
    • The headlamps are activated.

The high-mounted stop lamp contains 2 bulbs and is located in the center of the rear tailgate. The stop lamp is designed to operate in conjunction with the tail lamps whenever the brake pedal is depressed.

Circuit Operation

Voltage is applied continuously from the stop fuse to the stop lamp switch. Voltage is applied from the stop lamp switch to C4 cavity 5 of the Instrument Panel Junction Block when the brake pedal is pressed. Voltage flows through the Instrument Panel Junction Block , continuing through SP300 to the Center High Mounted Stop Lamp.

SP300 applies voltage to the following lamps:

    • The left and right stop lamps
    • The center high mounted stop lamp (CHMSL)

Backup Lamps

The backup lamps are designed to operate with the ignition in the ON position. Placing the transaxle in the R position closes the backup lamp circuit and turns the backup lamps on.

Manual Transaxle

On vehicles equipped with a manual transaxle, the circuit closes through the backup lamp switch. When the ignition switch is in the RUN or START positions it applies power to the gauge fuse, located in the Instrument Panel Fuse Block. Current flows from the fuse to Right Instrument Panel Junction Block. Current then flows through SP107 then finally going to the backup lamp switch cavity 2. When the switch is closed it allows voltage to be applied to Right Instrument Panel Junction Block through backup lamp switch cavity 1, which leaves the Right Instrument Panel Junction Block C1 cavity 2. After leaving the Right Instrument Panel Junction Block, current is split through SP302, to the rear combination lamp cavity 2. Ground is finally provided at the rear combination lamp cavity 3.

Automatic Transaxle

On vehicles equipped with an automatic transaxle, the circuit closes through the park neutral position (PNP) switch. When the ignition switch is in the RUN or START positions it applies power to the gauge fuse, located in the Instrument Panel Fuse Block. Current flows from the fuse to Right Instrument Panel Junction Block. Current then flows through SP107 then finally going to the backup lamp switch cavity 3. When the switch is closed it allows voltage to be applied to Right Instrument Panel Junction Block through backup lamp switch cavity 2, which leaves the Right Instrument Panel Junction Block C1 cavity 2. After leaving the Right Instrument Panel Junction Block, current is split through SP302, to the rear combination lamp cavity 2. Ground is finally provided at the rear combination lamp cavity 3.

License Plate Lamps

There are 2 rear license plate lamps located in the rear tailgate directly over the license plate. Each rear license plate lamp contains one clear, single filament bulb. The rear license plate bulbs will light when either the parking lamps or headlamps are activated.