Problem with courtesy lights

Did you bend out the prongs on the trailer side of pigtail yet?

some of them have a split in the middle that a knife tip works well to spread--

But be carefull not to spread em too far or they will snap...

 

Do you have one ore two trailer light cabels?

Usually there are two 7 pin cabels. One is the main, other for additional lightling, reverce lamps and other..

May be you have only main cabel.

There is one other cabel - trailer ABS/EBS - used not only for TABS/TEBS power supply, but for trucktor-trailer brake system communication via CAN and you will see additional unit on CAN with dashboard - MID 137.

It is not used for lightning but some drivers think they have pair of trailer cabels.

 

From my own experience I found that replacing the plugs every few years is benefic for preventing theese kind of issues. What I hate the most is that electrical problems start in the winter times when is almost imposible to go under trailer and scratch in the dirt.
I do have a Reitnouer 2007 trailer and the lights from the passanger side stopped working. Well I was lucky enough to be in California where the weather was kinda nice. Is very difficult for me to explain what I found in the back of the stop/position lights, in that "box" encapsulated. The dirt was 5 inch high and one of the plugs was disconected because of that.
So better do the check-up for the electrical system before winter.