hi new guy here, been working on my own truck for awhile but im finally stumped. i was hoping someone new more about the electrical system of a 2005 gmc sierra than me. my problem is i have a dim head light all the time, however when the auto headlights come on at night my truck fails to turn off when i turn the key to the off position. but if i turn the headlight switch to on the truck will shut off, also if i turn the high beams on, the truck will turn off. anyone have any suggestions?

welcome to the site jake.post up your problem in the proper section and we will get ya taken care of

welcome to the site, tough problem. the diagram says the control for all headlight functions is from the bcm, the ambient light sensor and the drl/run/headlight switch goes to the bcm as well. seems like something is feeding back into the ign circuit but im not sure where. seems like the bcm is where i would start looking for chafed wires, the problem may be internal to the bcm as well. seems like the dim light would have to be separate, the bcm controls relays for high and low that go through 4 individual fuses i would guess one of those fuse sockets may be loose/corroded or grounds are most times separate and the one for the dim one may need cleaned up

Welcome to the forum jake.

Welcome to the site. As mentioned, look at the BCM, look for any sign it got wet. Also check the fuse box. If this gets wet it will corrode on the bottom, so take it off and inspect it. With the problems your having it makes me think the truck may have been in a flood.

Welcome aboard Jake. Feel free to post your question in the proper section.

Welcome!

welcome!