This may seem unbelievable, but check bed light on the back of the cab to see if the bulbs are good and to see if any water has leaked into it. When the bulb out light for the rear right turn signal came on, I changed the bulb. and no improvement. Stopped into the dealer, and he said that if one of the bulbs in the light goes, this is how it is indicated. Changed the bulb and all was fine. They are interconnected some way so this could be it.
Elliott & Vicky, and Sadie the GSD copilot
2014 36RE, Onan, Titan disc brakes, 17.5 inch Sailun H tires, lots of other options
2013 RAM 3500 CC, LB, DRW, Cummins, AISIN, 4x4