SVTPaul

Interesting you were able to do that - do you have a picture of how you did that by chance? I had planned on using a quality posi-tap (not the kind you crush together with pliers) but your solution is better again. Thanks

Thanks for confirming this. I'm going to use a solid state relay (no mechanical switching so hopefully shouldn't be affected by the PWM signal) and tap into this circuit also. I'm concerned that if I try to tap into the switched ground, I may only get activation when high beams are turned on from the turn signal switch (flash to pass or manual high beam) and miss picking up BCM ground from auto high beam intellibeam. I don't know enough about the system and since you have confirmed a proven method, I'll copy you. Thanks again!

Thanks for the feedback! It says in the system description that the power supplied to the headlamps from the LCM is PWM. In the below diagram from GMupfitter, it looks like there's a white wire (524) for high beam activation going to the BCM from the turn signal lever at X2 32. I'm new to all this and not sure if that's a pin location on the BCM etc...guess I better read up on what all the symbols and numbers mean. But I'm thinking if I tap into that wire to ground the relay trigger signal it might do the trick? It does also show a white wire (711 & 311) from the LCM to the left & right headlamps on the following page - that must be the wire you tapped.

Hey, first off thanks for posting this! I'm going to be wiring in a light bar on my father in-law's 2025 Sierra 1500 Denali...figured it was going to be as simple as triggering a relay off a fused circuit for the high beams in the engine compartment fuse box but damn these vehicles are getting far more complex than they need to be!! I am guessing the white wire from the LCM gave you 12V hot wire? From what I read this is a pulse width modulated voltage that could possibly cause issues with the relay (as it is not the ideal type of power for a relay) or the LCM (concerning). Did you happen to find which wire goes to ground from the BCM when the high beam circuit is powered? I'm hoping to find that and run 12V ignition source to the relay trigger and ground it to the BCM wire that goes to ground when high beam is activated. I'm starting to look around gmupfitter.com which I'm also new to and was hoping to avoid spending more hours researching this than doing the actual installation!