Brown wire, pin 22 on the 56-pin connector C1 of the PCM.
This is all I can find in the service manual, I don't know if it comes into the car or not.
Everything inside the car uses GMLAN.
If that doesn't work, my info says something else...
Speed Sense brown (3.5 or 3.9L only) PCM, blue plug, pin 22 or 39
Notes: The PCM (Powertrain Control Module) is in front of the battery on the driver side fender.