For anyone struggling with the Illuminated GMC grill badge having an 8 pin connector while the head light has a 12 pin connector below are the two wires I successfully tapped into to make it work.
2025 GMC Sierra 2500HD Denali Ultimate
12pin driver side head light harness
Pin #1 Black = GND
Pin #6 White/Yellow Stripe = Running Lights
Tip: Turn the wheel to the right and remove 5 of the wheel tub screws. And fold tub enough to get at harness.