Circuit/System Description
WARNING: This page is about a different car, the 2008 Buick LaCrosse and 2008 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.
B+ is applied at all times to the park lamp relay. When the headlamp switch is placed in either the PARK or HEAD position, ground is applied through the park lamp switch on signal circuit to the body control module (BCM). The BCM then applies a ground to the park lamp relay control circuit. This energizes the relay and applies voltage through the park lamps.