Circuit/System Description
WARNING: This page is about a different car, the 2011 GMC Yukon, 2011 Chevrolet Tahoe, and 2011 Cadillac Escalade. However, it is still accessible from the selected car via links, so may be relevant.
The Run, ON, and START Power signals connect the serial data gateway module along with numerous other modules to the vehicle 12-volt system through a fused relay in the fuse block - underhood. This relay is closed by the Body Control Module (BCM) based on the key being in either the RUN or START position.