Tail light issue

Best unprofessional guess is that you have either a dead short to ground, or, a burnt out ground link somewhere in "one" of the hot wires from the fuse panel that feed the lighting circuits. Use brakes while using turn signals? Use brakes while emergency blinkers flashing? Check brake light switch which is normally open, hot from stop fuse through brake light circuit on one terminal, and run straight to ground at the other terminal. When you use the brakes the switch closes to ground to complete the circuit and send current through both the brake lights and to the brake light indicator. The switch to your blinkers, headlights and rear lights are on a separate fuse, don't know what that might be in your Yukon. This is normally closed switch which is hot on one side and connected to the lighting circuit on the other side. Current flows from the switch through the lights to ground. Basically allows current to flow through a single conductor to a common appliance in one direction, "or" the other direction. But not in both simultaneously, because current will always follow the path of least resistance to ground. Hope it's the brake switch, cause the other circuits are subject to have the same type of possibility in any one of the interconnected switches, sensors, timers, relays and modules in the lighting circuit.