Headlights, high and low beam, quit working on 1999 GMC Yukon?

[ehad46]

My sisters Yukon has mysteriously lost both high and low beams on the headlights. I was wondering what would cause this and if there may be a relay that went out I could change.
Some of her friends looked at it and said it was an electrical problem, but they aren't mechanics and don't have a lot of knowledge.
Any help would be appreciated. Thank you!

 

[chevyriderk15]

may be the switch, the parking lamps and headlamps are probably separated in the switch and the section for the headlamps may have failed, i have a 94' chevy and that's what hap pend to mine.....just something to check into

 

[Mikey]

Headlight dimmer switch gives more trouble and controls both hi and lo beams as well as all headlights at same time.