CODE4

Just to throw some information on the mystery splice - it is a dealer installed flasher unit for the 3rd brake light. Pressing the pedal causes the CHMSL (3rd brake light) to pulse a few times before going solid. I unplugged the ground reference from the T-Tap and tested it and confirmed. Still looking for any information regarding the surveillance switch ability and related information on my original post, if anyone can assist. Thanks!

Evening everyone, name is Dave and new to the forum. Long time member over on the Duramax world, as I have a 2012 2500HD as a personal vehicle. Recently was issued a 2021 2500HD Custom with the gas burner for a work truck. First thing I ordered was the 9L7 upfitter switch kit (has new knee bolster with the 5 AUX switches, and all related wiring and fuse block). Over on the GM Upfitter site I grabbed the latest Body Electrical PDF and poured through it. Looking for assistance specifically on circuit 6821, a white and violet wire in cavity 4 of the X260 Aux Fuse block harness. From what I can find the Surveillance switch signal is a provision for law enforcement where a user supplied switch toggled to ground will disable all exterior lighting and interior dome lamps, as well as dim instrument panel lighting to a minimum. I am always one of those guys that rolls the headlight auto switch to the CCW position EVERY time I start as I hate DRLs or the truck doing ****** without me telling it, etc. Anyway, when climbing under the dash of my truck I found that position 4 that should have the white and violet wire is empty. Curious if anyone has dove deep into this and looked for such a wire. I fired off an email to GM Upfitter assistance and will see what I can get back. Also, I attached a picture of something odd I found under the dash. An interesting splice to a small heatshrunk board, with a signal to ground. Checking the electrical manual shows the signal being spliced is for brake light circuit. Not sure what to make of it as it clearly looks like an after thought on GMs part. Curious if anyone else sees something similar. My truck has a build date of 07/21 - probably one of the last 21 models to be built.