Chasing No left turn Signal on Trailer With Ram Truck

OK guys I have a new issue with this 2013 Ram 6.7. I had to pack some bearings in my utility trailer and afterward, I hooked up the truck and plugged into it to see about lights on the trailer. Found out left signal light not working. Later that day I connected our Subaru to the trailer and everything works. So then I hooked up another trailer I have to the truck and same issue, no left turn signal. The truck has at the bumper a seven pin, and 4 pin connection (all in one). I then tried the seven pin inside the bed to isolate which connector is bad, and guess what, no left signal there as well. So now the issue moves to wiring harness at the junction under the truck where the two split to see if there is power there.

Can anyone here tell me any tips in chasing this, or thoughts on if there is no power at the junction where you would go from there?