PTO Relay
WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The PTO Relay is located on the side of the underhood fuse block. The secondary side of the relay is supplied with voltage at all times through the Fog Lamp fuse. The PTO switch controls the voltage to the primary side of the PTO relay while the PCM controls the ground.