Sounds like a wire issue best way to find it (as long as you already know that the fuse is good)is to start at the connector for the tail lights and check for both power and ground then trace your wires back to the next brake in the wire and check again. If any insulation has ever been stabbed a bubble of corrosion can develop and cause to much resistance for any current to pass aswell as if a wire has been pinched it will cause a break inside of the rubber that you will not be able to see so as you trace your wires you should be giving them a slight tug and watch for Streching that would reveal your issue if the wire snaps from you pulling on it then it was already broken