Battery voltage is applied to the headlamp bulbs at all times. The headlamps are controlled by supplying the ground for the lamps through the turn/headlamp switch assembly. When the turn/headlamp switch is in the ON position, the ground is supplied through CKT 150.

The body control module (BCM) controls the daytime running lamps (DRL). The system allows the high beam headlamps to operate at a reduced intensity when the following conditions exist:

The BCM turns on the system by grounding CKT 592. This action energizes the DRL relay. This condition allows a reduced voltage across the headlamps by placing both high beam headlamps in series with each other. When the headlamp switch is turned ON, the headlamps operate normally.

The park brake provides an input to the BCM. When the park brake is in the ON position, the daytime running lamps remain disabled until the park brake is moved to the OFF position or the vehicle speed is above 3 mph.

The fog lamp switch provides an input to the BCM. The BCM enables the fog lamp relay under the following conditions:

When the headlamp switch is in the HEAD position, ensure that the high/low beam switch is the LOW position in order for the BCM to enable the fog lamp relay.

The BCM controls the headlamps and the park lamps by energizing the automatic lamp control relay. The BCM uses an ambient light sensor for the following reasons:

The BCM energizes the park lamp relay in order to turn ON the exterior lamps. Refer to Exterior Lights Circuit Description .