This looks like a good place to start - I'm accepting the answer.
If i have one or two more questions about the same subject, do i have to pay again?
Seeing that this is the factory wiring, there won't be a splice between the wires to the tail lights and the 7-way connector. I am just hoping its not the wiring harness since it runs inside the frame !!!
Seeing as the truck left turn/running lights work, but not the trailer left turn/running lights - what else would you think it could be besides the 7.5A fuse?