The logic resides in the BCM. Here's the Headlight Circuit Diagram. Check the volatage going into the BCM (lower left side of dash) on the orange wire 192 going into position 21x3 and coming out on the dark green/black wire 1317 from position 11x4. If you bypass the BCM by connecting those two wires directly, you should get what you are aiming for.
2008 GMC Sierra 2500HD SLE2 LMM 2WD Crew White/Ebony
Denali Ultrasoft Leather Seat Upgrade
4" MBRP with muffler
Quad Stealth 2 "Stock no DPF" program
Ranch Hand Grille Guard
Westin Nerf Bars
Recon Clearance Lights