I own a 2009 Ford F-150 XLT SuperCrew 2WD, I have done this list of things so far to solve my problem

The right rear blinker & brake lights do not work
Tail & backup lights do work
All other lights on the truck work
The blinker indicator in the dash blinks rapidly
Replaced the bulbs, still does not work
Moved right side bulbs to the left side, the bulbs are good
20 amp fuse, in slot #6, under the dash is good
The relay in slot #38, under the hood, clicks loudly and rapidly, even when
replaced with a known good relay
Testing the bulb socket indicates electrical current to each bulb socket
The electrical current pulsates with the blinker signal
Ground wire under the truck checks out to be clean and secure

If you have any other ideas to try I would appreciate hearing from you.