Problem with outside lights

Hi there. Just recently on my way back from camping my running lights wouldn't work while I was towing my travel trailer. The back lights would turn on if I hit the breaks, but the running lights, the ones that are just supposed to stay on while your headlights are on, would not work. I tried blowing out both sides of the connection at the hitch and tried all different settings on my trucks headlights. Nothing. I looked at the fuse box in my TT and everything looked good. I've only had the TT a few months, so I'm a total rookie. Any help would be greatly appreciated!! Thanks!