rear lights don't work

Hello all, new to this forum. I have a 1998 f150xl which was purchased used several years ago. for the last 2 weeks I have been having intermittent operation of my passenger rear turn signal. yesterday noticed I didn't have any rear running lights when I turn my lights on.the headlights come on. I have brake lights. and the driver's side turn signal works. passenger side front turn signal blinks rapidly, but nothing in the rear. all fuses check ok. I'll be crawling underneath to check the wiring today. Thanks

My guess would be a ground wire is battling rust at the connection where it is bolted to the frame.

well, after checking the wires found out that it was a loose connection where the rear harness connects to the main harness on the driver's side frame. thanks for responding.