I am a new member, first post. Excuse me if I jump right in to an issue I require assistance with at the moment.

I recently installed after market cab lights on my 2020 High Country 1500. I connected them as per the instructions form Boost Auto to the pin in the BCM that also controls the license plate light circuit. The license plate lights and all the DTR lights and parking lights all come on when you unlock the truck. They will stay on if I turn on the headlights, that is until I start the truck. At that point the parking lights/license plate light/DTR lights all turn off. They come back on if I recycle the ignition but again fail if I start the engine. I will throw in one more oddity, the slider back window open a crack occasionally at start up.

I have pulled every fuse in all 3 fuse boxes and checked to make sure they are not blown.
I have disconnected the cab lights from the BCM
I have removed the battery cables, jumped them together for 10 minutes and reconnected them, at which point I had to reset all of the presets so I know I cleared it.

What have I done? I do not own a code reader but I suspect I made it angry. Any ideas other than GM Therapy?

 

The check engine light will be on if there are codes to be read with a code reader. Is that on?

I can only speculate, not having a wiring diagram for that truck, but wonder if you damaged that output of the BCM by overloading it with too big a load. It was designed for all the stuff on it from GM, and not for an additional lighting load.

I can't explain why it works when you turn the key to on, but then dies when you start the engine. I do know that with most of my vehicles, stuff like cab lights cut out while the engine is cranking, then come back. If the BCM output is damaged, it may not be "holding" the state for the various lights.

Are the headlights working and turning on and off while the truck is cranked? Does turning those on and off affect the license plate light or anything else on the circuit?

 

I just went out and turned on the lights without starting the engine, all of the lights are on including the license plate markers. I did not the back window opened about 2-3" (weird). AS I watched the plate markers went out, came back on for a Monet and then turned off. The DTR lights were on but went out with he license plate markers, but thye do illuminate when the head lights turn on. I went to close the rear window and the switch did nothing. I cycled the ignitions and it worked fine again. Crazy

 

No check engine light, to be clear. I went out just now to play with it some more and the rear window opened and refused to close. When I tried the switch I noticed the courtesy lights in the overhead console dim slightly. I thought that odd and pushed on them to turn them off. When I turned them on again they started flashing,, one then the other, back and forth. I turned off the ignition and they continued to flash. I pushed them to turn them off so the battery doesn't wear down. Whatever ghost I picked up it has inverted friends over.

 

Wish I could help more, but I have no experience with the recent model years of GM trucks, so am out of my depth. Everything you are describing to me seems tied to things that are controlled by the BCM, so I still have a nagging suspicion something happened to the BCM with your recent addition of cab lights. But that is about as far as I can go. Does seem you have unleashed the gremlins into your vehicle at this point...

 

I have an appt with my GM tech on the 21st. Hopefully they can put the jeanie back in the bottle. Thanks for your help.