Daytime Running Lamp (DRL) Dimming
WARNING: This page is about a different car, the 2003 Pontiac Montana, 2003 Oldsmobile Silhouette, and 2003 Chevrolet Venture. However, it is still accessible from the selected car via links, so may be relevant.
When the Daytime Running Lamps (DRL) control module has the headlamps ON and the park light switch is OFF as in night mode, voltage is fed back to the headlamp switch assembly through the park lamp supply voltage signal. This allows the dimming circuits to function as stated above.