For one of the few times I ventured to open the hood of my Denali. I was going to attempt to change the headlight bulbs to a clearer bulb and my fog lights underneath...Yup I'm still scratching my head...how much has to be disconnected to replace the headlight bulb???

See if this helps.......this details a Chevy Silverado, Suburban, etc. but your Denali should be similar. This shows replacing a DRL, but also shows how to remove a headlamp.

http://www.geocities.com/tbuckit1/DRLrep.html

-slacker