Running lights not working - how to troubleshoot?

I did take a small file and hit the trailer side connectors with it to get a clean(er) base. I did not do the truck side.

You know..... seems like I was having to wriggle it a bit a while back to get it work. Sounds like a good cleaning is in order.

Westend - are you saying your truck has a separate fuse for just the lights? and brakes and signals is on another? If it's a single fuse, then I don't think it's that as I had turn signals and brakes, just no running and tail lights.

Thanks guys.....