R/R brake light does not work.

Check for a wiring issue to the right rear. Test for power and ground at the socket; trace backwards for whichever circuit is malfunctioning. Check especially for any "flex points" of the wiring harness at the lift gate possibly also for pinched or damaged wires.

IF red color only for brake and signal lights - (no amber signal) - - IF left rear rear signal light is functioning properly- then the brake light should also function properly - it's the same wiring circuit and bulb element for both!! Since brake light circuit must pass 'through' the signal light switch 'before' it goes to the rear lights - - it is a very strong possibility that circuit is NOT passing 'through' the signal light switch - which will prove to be a failed combination switch .. It is kinda difficult to understand exactly how this works - however the 'repair facility' will be happy to give you a *hands-on* demonstration when you take it in for this repair.