GM Service Manual Online
For 1990-2009 cars only

Turn Lamps

When the ignition switch is in the RUN or the START position, voltage is applied through the TURN/LPS fuse to the normally closed contacts of the hazard switch. A single flasher in the hazard switch performs the following functions:

    • The turn signal operation
    • The hazard flasher operation

When the turn signal switch is in the LEFT position, voltage is applied to the following components:

    • The left turn indicator
    • The left front park/turn lamp
    • The left rear turn lamp

The lamps immediately turn on and flash as the flasher opens and closes the circuit. If a bulb is in need of replacement, the turn lamps will flash at twice the normal rate.

The voltage supplied to the left front park/turn lamp is also applied to the left front marker lamp. When the turn/headlamp switch assembly is OFF, the left and right front marker lamps find a path to ground through the left and right front park/turn lamps. The front park/turn lamps provide low resistance paths to ground. The left front side marker lamp also flashes with the turn lamps. The lamps used for the ground path will not flash because the voltage drop across the side marker lamp is much higher than the voltage drop across the other lamps.

When the headlamp switch is in the PARK or the HEAD position, voltage is applied to the following components:

    • The marker lamps
    • The parking lamps

When the turn switch is in the LEFT position, the following conditions exist:

    • The left marker lamp has voltage at both connections.
    • The left marker lamp does not light.

When the flasher stops the voltage to the turn lamp, the following conditions exist:

    • The marker lamp is grounded through the turn lamp.
    • The marker lamp lights.

The left front marker lamp flashes on when the turn filament of the left front park/turn lamp turns off. The left front marker lamp flashes off when the turn filament of the left front park/turn lamp turns on.

When the turn switch is in the RIGHT position, voltage is applied to the following components:

    • The right turn indicator
    • The right front park/turn lamp
    • The right rear turn lamp

The lamps immediately turn on and flash as the flasher opens and closes the circuit. If a bulb is in need of replacement, the turn lamps will flash at twice the normal rate.

The voltage supplied to the right front park/turn lamp is also applied to the right front marker lamp. When the turn/headlamp switch assembly is off, the left and right front marker lamps find a path to a ground through the left and right front park/turn lamps. The front park/turn lamps provide low resistance paths to ground. The right front marker lamp flashes with the turn lamps. The lamps used for the ground path will not flash because the voltage drop across the marker lamp is much higher than the voltage drop across the other lamps.

When the headlamp switch is in the PARK or the HEAD position, voltage is applied to the following components:

    • The marker lamps
    • The park lamps

When the turn switch is in the RIGHT position, the following conditions exist:

    • The right marker lamp has voltage at both connections.
    • The right marker lamp does not light.

When the flasher stops the voltage to the turn lamp, the following conditions exist:

    • The marker lamp is grounded through the turn lamp.
    • The marker lamp lights.

The right front marker lamp flashes on when the turn filament of the right front park/turn lamp turns off. The right front marker lamp flashes off when the turn filament of the right front park/turn lamp turns on.

Hazard Lamps

Voltage is applied at all times to the normally open contacts of the hazard switch. When the hazard switch is in the ON position, voltage is applied to the following components:

    • The front turn lamps
    • The rear turn lamps

The following components flash on and off:

    • The turn lamps
    • The turn indicators

The front marker lamps flash when the hazard lamps are on. Refer to the Turn Lamps Circuit Description above. When the headlamp switch is in the OFF position, the front marker lamps flash on when the hazard lamps are on. When the headlamp switch is in the PARK or the HEAD position, the front marker lamps flash when the hazard lamps are off.

When the hazard lamps are turned on, the hazard switch flashes.

Park/Marker/License/Tail Lamps

Voltage is applied to the turn/headlamp switch at all times. When the turn/headlamp switch is in the PARK or the HEAD position, voltage is applied to the following components:

    • The park lamps
    • The marker lamps
    • The tail lamps
    • The license lamp

The front marker lamps are grounded through the turn filament of the respective front park/turn lamp. The front marker lamps light as a result.

The automatic lamp control function turns on the park lamps and the headlamps. This action occurs when the ambient light sensor in the BCM determines that the exterior lamps should be turned on based upon the amount of available ambient light. When the BCM grounds the park lamp relay, voltage is supplied directly to the parking lamps, bypassing the turn/headlamp switch assembly. When this action occurs, the following conditions exist:

    • The automatic lamp control relay is grounded.
    • The headlamps turn on.

The lamps turn off when the BCM does not ground the park lamp relay or the automatic lamp control relay. This action is caused by the following conditions:

    • The available light reaches a predetermined level.
    • The ignition switch is turned to the OFF position.

Stop Lamps

Voltage is applied by the brake switch at all times. When the brake pedal is depressed, the brake switch closes. This condition supplies voltage to the following components:

    • The high-mounted stop lamp assembly
    • The left tail lamp
    • The right tail lamp
    • The left stop lamp
    • The right stop lamp