Circuit/System Description
WARNING: This page is about a different car, the 2006 Buick Lucerne. However, it is still accessible from the selected car via links, so may be relevant.
Battery voltage is applied at all times to both the coil and switch sides of the PRK LAMP Relay. When the headlamp switch is placed in the PARK position, ground is applied through the park lamp switch 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 both park lamp fuses and to all the park lamps.