No trailer lights

check your pigtail

 

Your truck might be running power to the trailer thru relays, not fuses, check those as well. Get a test light and start checking the plug on the tractor for power, if all is good there go to the end of the pigtail and check for power there. If that all checks out good, pull the receptacle off the front of the trailer and look for loose, corroded, or broken wires. Just because it is almost like new does not mean it can't be the problem.

 

Where your pigtail plugs into the tractor, unplug it and lift up the cover, there are pins in there. Take your test light and ground it to your frame on the truck, turn all your lights on and see which pins have power and which ones don't, your trailer might have a diagram on it to show you which pins are for what.

 

You can check real quick if the problem is in the truck or trailer by testing for power at the trailer cord with your test light. Check with it disconnected and the lights on. This picture sucks, but it was the best I could find. The black wire is normally your tail lights, brown are the clearance markers.

 

Always check the source of the power first, meaning the tractor, then work your way back from there. I had a problem very similar to yours a while back, ended up being a corroded wire on the back side of the receptacle on the tractor.

 

Pull the boot back and check for corrosion. I kept losing my brake lights turns out the plug on my deckplate box was all green. Replaced it and everything works better and sees to be a bit brighter too.