Sounds like same type of problem from a post from a couple of years ago on grand design:
2-23-2016, 12:10 PM #1
HankABG
Reflection Electrical Fire
"We took delivery of a 2016 Reflection 27RL 5th wheel on 2-11. It had an electrical fire under the right slide out on 2-13. ...
Looks like it started at a 110 volt junction at the right frame rail under the right rear slide. Burned the junction as well as the wiring to the slide. Not sure what else was affected."
I checked several on the Molex SPCCs (Self-Contained Power Connector System)on my FW under the LR/Dinette Slide, found some with faulty assembly by the factory, still have several near basement to check.
I was going to add a pict or 2 but recent the photobucket 3rd party hosting $399/yr thing has turned me off online pictures.