2007 GMC Yukon battery dead this morning. Jump started, headlights will not shut off. Cannot turn headlights off manually with switch. Checked relay, fuses-ok. Unplugged BCM, multifunction switch, headlight switch, headlights stay on. Going by the wiring diagram there is 1 wire that runs from low beam relay to BCM. I am thinking 2 options- bad wire or something bad inside fuse box. Anyone have any other ideas?

Forgive me, but it'* not the driving lights?

My sonoma headlights are on anytime the engine is running (@ a lower voltage)

Were any extras added recently? - something that may have been spliced into a convenient hot/ground wire?

Or as you wondered, short in fuse box, tho' that would be my last guess - I'd imagine 12volts from the fuse goes to headlight relay, the switch closes the relay sending on to the headlights.

luck,greg

No Greg, not driving lights. The DRL is also a separate relay. Tried swapping relays. And the headlights do not shut off with engine not running, key out. Thanks for your thoughts.

It sounds like a short somewhere. Have you tried disconnecting the battery to let them go out, then reconnecting it?

dont have time to look in the drawings but most of the relays are ground controled so if the control wire for it was chafed touching ground it would be always on

Yes, we did have battery unhooked. Did not help. We agree the wire to the relay is gounded somewhere. Just have to find it.
Thanks for the input.

I had this same issue and found that when I pulled the top of the under hood fuse block toward the driver side fender the lights went out, then came back on when let go. I removed the fuse block, cable connectors, and fuse block housing/mount. The wiring harness under the housing was routed over and rubbing against an edge of the fender body. I taped a piece of old inner-tube over the fender edge for the wiring harness to rest on, then put everything back together. So far problem solved!