2001 yukon denali xl. Suddenly no headlights (both), fog lights or dome lights. All signal and clearance lights are working. Any help, much appreciated!

Here's a link to see about your light fuse. Interior Fuse Box Location 2007 2013 GMC Yukon XL 1500 2007 GMC Yukon XL...

If front park lights are working highly unlikely headlight switch is the issue. Is the vehicle equipped with a trailer towing package and wiring to the rear? I would start there. This vehicle may also have a taillight module located under the vehicle on the passenger rear attached in the wheel well area that goes bad

I'll try to help, everytime something gets replaced on these yukons, that circuit needs to be RESET ! Is there a reset button, on your steering wheel, to reset a variety of functions ? , check owners manual, or call your dealer for better advise

The alternator isnt charging or starter is grounding ou

sound like battery has weak or battery terminals and post need cleaning. have battery charged and checked, if battery good. alternator not charging battery. if battery over 5 years old more likely battery is bad.if battery too weak head lights wont turn on battery dead this time of year if battery old. cold weather will finish it out.

need to know if it is a hid or regular light as the procedures are differnt

get you alternator checked

FROM LUSTY KID:

Check your bulbs first, I have lost both headlights on my ford at once on account of the bulbs burning out at the same time. Same thing probably happen, you have one filament out. The lights can work, but if the filament for brake is burnt, you don't see brake lights.

As for the cruise control. Check fuse box first. If OK check vacuum hose to actuator in engine compartment for starters.
Advise:

Check the headlight fuses in the engine fuse box compartment. Not sure if the lights have relays, but they will be clearly mark in the inside of the top cover for location.

Yup - you may need to get the grilles and such as well...