RepairPal Certified shops can diagnose and repair your 2006 GMC Yukon XL 1500. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.
Brake lights get activated by a switch on the brake pedal or under the hood (depending on the vehicle). This switch can fail, or the wiring connector that plugs into it can melt. Inspect there.