The running/marker light circuit on my rig has been acting up and very intermittent. I could never seem to find the fault because it would work fine at the campground and only sometimes act up.
When it was bad it would blow a fuse in the truck. I finally found it. It started to act up consistently when hitched. When I would raise the hitch and take the weight off the truck it would work, lower the trailer back on and the lights would go out.
The wire leading from the front driver side running light to the other side runs through a empty space above and forward of the front storage and had worked its way between the frame and the front siding. When the weight was on the truck I guess it was enough to pinch this wire and short it out.
Weird one.
Ray