SB29 feeds a big yellow/red wire directly to the J519 module (the Body Control Module, sometimes still called a Comfort Convenience Module) under the dash, to pin 42 of the T52c connector. There are three connectors on the BCM; black, white, and brown. The T52c is the brown one.
But this may not help you, as the BCM uses several different fused feeds input for a variety of different outputs, and they are not broken down in the wiring diagram as to which is for what. It could be something on the output side, it could be the BCM itself.
What you might do, is unplug that connector, and see if your dead short goes away. If it does, then you know the short isn't in the wire TO the BCM.
Next would be to try and depin that wire, so you can plug that connector back into the BCM, and see if you can communicate with it and see if it can give you any clues.