Circuit/System Description
WARNING: This page is about a different car, the 2007 Buick LaCrosse and 2007 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.
The body control module (BCM) supplies a 12-volt reference to the ignition switch. Based on the position of the ignition switch, the 12-volt reference provides feedback to the BCM to determine ignition switch position.