Hmmmmmm. I'm sitting in my lazy-boy staring at the overhead light in the slide-out dining room, wondering what I'd do in your predicament.
It's true that the wiring is nested between the interior ceiling panel and the external roof panel. So other than a possible short piece of wire attached to the fixture itself, it might be difficult to trace it much farther from the light fixture end.
However, if you remove the fixture, you COULD observe what happens to that portion of the wire. Does it get tugged on? Is the short at the fixture itself? If not, then you can assume a "pinch" is elsewhere.
I'll see if I can find where the wire goes from there. I bet it is routed in the vertical wall and then exits the slide underneath in the flexible loom. That would be the other more likely spot to look. If so, you might be fortunate and find exterior access to the culprit.
Good luck! Let us know what you discover.
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