Circuit Description
WARNING: This page is about a different car, the 2006 Pontiac Montana SV6, 2006 Chevrolet Uplander, and 2006 Buick Terraza. However, it is still accessible from the selected car via links, so may be relevant.
The body control module (BCM) controls the horn relay by grounding the control circuit of the horn relay coil. When the horn relay coil is grounded, the horn relay contacts close, applying voltage to the horn via the horn supply voltage circuit.