Trailer tail lights stay on when nothing is powered

What truck? Issue could very well be there.

 

Both trucks with same issue on the same trailer tells me the issue is in the trailer

 

You probably have a wire crossing over from the trailer 'hot line'. The blue wire in the 7 way is ' hot ' always, that is so if you need power in the van for lights . You pick up the hot line and run through a switch then , to 12 v lights so even with truck off you can see in the trailer. Pull the trailer 7 way out and look closely , ground is loose and center pin wire is more than likely crossing over to marker. It should be feeding back to truck cab lights or the marker there, may be very dim but see if their on also. Then unplug , if they go off , then it's the trailer for sure. Sorry, I mean the tail on tractor.

 

BINGO!!!! You are barking at the right tree.

 

I'm am betting you have a boogered up green cord where wires are contacting. It could also be in the box the cord plugs into.

 

Ground somewhere or a wire, probably on the abs. I’ve already spent a few hours trying to fix old wiring on my trailer but I finally broke down and bought 2 new junction boxes to rewire Each side from the previous owners “my buddy great with wiring” layout, if you run in salt it kills everything.

I pulled the constant abs wire out of the junction box and wrapped it in tape, but my old truck technically doesn’t need it, it still cycles with the brake lights, I’ll fix it on one of the nice spring days coming up instead of during a snow storm

where do the bottom rail lights tie in? On the side, the rear, or a junction box?