Why would the driver side turn signal on the trailer work, but not the passenger side?

I was going to suggest the same thing. I drive a Volvo and my passenger side turn signal lights went out. Swapped trailers and still had same problem. Went and got new pigtail cable, hooked it up and still same problem. THEN, I went looking for the fuse. Yep left and right different and right side was blown. New fuse, problem fixed.