I unscrewed the left brake light (2 bolts) removed it from the truck, and used a tap connector to connect the reverse wire from the tailgate bar to the brown wire in the reverse light. There are 3 wires connecting the brake lights. The 2 black wires are ground, brown was power.
MJIYA LED Truck Tailgate Light Bar Strip, Red Brake Light White Reverse Running Turn Signal Tail Lights for Pickup Trailer Jeep SUV RV Van Dodge, No Drill Install (1 Row 48 Inch)