Yup, I smell a modification...
I'd bet if you take the plate down off the ceiling, you will (hopefully) find another wire there, but unfortunately probably with the end cut off, because it would have had to get back through the hole in the plate somehow.
From the looks of the mod, the trailer was parked more long term in a spot where southwest would be behind your back in this pic. The sat dish could be hooked up to that connection and set up on a tripod off the front of the trailer.
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9467.8 (as of 5/26/19)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR