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Discussion Starter · #1 ·
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.

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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.
 

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I have the same thing in my 21 truck. I thought it was installed from my dealer as to make my 3rd brake light pluse like three times when I hit the brakes. Dealership put that on all there vehicles they sell the said. Offered to take it off. But I told them if that's the only thing your up charging me for and not the list of other things other dealership do. Keep it on there. I bought my truck in Minnesota..

Now I am very interested, if it's something else.
 

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Discussion Starter · #3 ·
I have the same thing in my 21 truck. I thought it was installed from my dealer as to make my 3rd brake light pluse like three times when I hit the brakes. Dealership put that on all there vehicles they sell the said. Offered to take it off. But I told them if that's the only thing your up charging me for and not the list of other things other dealership do. Keep it on there. I bought my truck in Minnesota..

Now I am very interested, if it's something else.
Surfdog - Good call. I tested mine and unplugged the ground T-Tap and sure enough the 3rd brake light goes on solid. Plug it back in, and it pulses before going solid. Mine was built in Michigan (I believe all HDs are) and put on a train to Florida where I got it.
 

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Surfdog - Good call. I tested mine and unplugged the ground T-Tap and sure enough the 3rd brake light goes on solid. Plug it back in, and it pulses before going solid. Mine was built in Michigan (I believe all HDs are) and put on a train to Florida where I got it.
Yeah all HD'S are built in Flint Michigan. I bought my truck in Minnesota and drove it back to Florida. I live in Jacksonville area. Great you tested it. I didn't test mine at all thought that's what it was. I added some light mods from boost auto. And saw that down there. My truck is a LTZ
 

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I’d love to have this wired up myself. Have you considered buying the pins and inserting it into the proper hole in the plug? Just because the wire isn’t there doesn’t mean it’s not possible to add it.
 

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Discussion Starter · #6 ·
I’d love to have this wired up myself. Have you considered buying the pins and inserting it into the proper hole in the plug? Just because the wire isn’t there doesn’t mean it’s not possible to add it.
If the wire was there on the truck side of the harness, I agree I'd order the appropriate terminal and wire it in. However, the circuit itself is not there on the IP harness, so I would need to back track to another harness connection as indicated on the upfitter manual at this point. I did receive an email back from GM and they said:

Your vehicle is not calibrated for the surveillance feature...that feature is only available on the Police and Special services vehicles. FYI the wire was removed from the X260 connector as it was never specified to be in that location...engineering thought they were doing us a favor. Sorry you'll still have to disable the lighting by the switch.
 
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