There could also be a fuse or wire just missing. In our 2021 Milestone 386BH we had a "mystery fuse", an inline (on the wire - not on the panel) fuse holder in the front garage near the front right landing gear leg. Maybe you should look for one as well. It wasn't super obvious, it was partially tucked behind a carpeted trim panel in the storage bay. I was curious what it was so I threw a fuse in it an lo and behold! The solar started working.
Bear in mind these factory solar setups are almost universally tiny. Mine was a 20W panel which is almost a joke on a fifth wheel - it'll "tend" your battery but not much else. When I Installed our bigger solar setup I didn't even bother removing (or reusing) it. I just put the new panels right over the old one.
