2003 Ram parking lights

My 03 Ram's left side tail lights and front parking light are out. The right side is fine. Brake, headlights, turn signals are all working. I don't think that the front and rear bulbs are tied together, and the fuse appears to be ok since the right side is working. I've unplugged my add on round trailer wiring. Any suggestions?

Trace the wires, look for chafing or a break.