Right rear brake light!

Every light works except the right rear brake light. Yes, I changed the bulb. It has a factory plug and play trailer light harness that is good on it. All of the trailer lights work also. Any advice?

Get a test light and start probing. It needs power and ground... find out which one it doesn't have.

check your turn signal switch...

Just had the same exact problem on my work truck, and the mechanic told me its a good indicator that the turn signal switch is failing or has a burnt spot on it.

I had the same problem and it for a year. Finally took it to a shop abd what they reported to me was a short in the harness behind the headliner. I'm not sure how accurate that is because I didn't witness it, but might be something to consider.

Wire for right brake light has a terminal block in left rear 1/4 panel, pull the inner plastic panel for access. Trailer wiring attaches there and from that block wiring runs thru headliner to right side. Somewher after where the trailer wiring is attached and the socket for right brake light you have a broken wire. Start with a test light at the socket and work your way back to this terminal block. One hint the grounding inside the socket is poor at best when working properly. I have replaced these sockets with aftermarket GM, Ford, Chrysler sockets. Check the ground by touching a wire to the outside metal area of the bulb (with bulb in socket) to a ground. That is most likely where you will find your problem.
Al