Does your trailer have satellite wiring? If so there is probably a jack plate with two coax connectors on it and there should be a short jumper between the jacks.
If that is all normal, then in my experience, it is more likely that someone has reconfigured the wiring. The coax from the outside should run directly to the panel with the switch and LED. If you don't have a manual for the antenna, and assuming you have the original antenna, Google Winegard Sensar to find one. It has a diagram of which connector is which on the circuit board. If I remember correctly it is the jack in the center of the circuit board.
My trailer had been rewired by placing an extra splitter in the wall behind the jack with the switch and connecting its input to the output of the switch that went to the other TVs in the trailer. The cable to the other TVs was on one output of the new splitter and the cable to the outside was on the other port of the splitter. This allowed the cable to be used to send a signal from the antenna to a TV outside the trailer instead of as a cable input.
The giveaway is that there is a splitter behind the switch panel and nothing connected to the center jack on the circuit board. The easiest thing to do is pull that switchplate and check the wiring behind it. You could also set the system to antenna and hook up a TV to the outside jack to see if it works. Less work than pulling the switchplate, but if that is the problem you will have to pull it to fix it.
Oh, put the trailer in storage mode or disconnect the battery before pulling the switchplate. It is very easy to short the 12 volts when pulling the plate and that will blow a fuse. Don't ask how I know....
“You cannot reason someone out of a position they have not been reasoned into"
Al, K5TAN and Missy, N4RGO WBCCI 1322
2002 Classic 30 Slideout -S/OS #004
2013 Dodge 2500 Laramie 4x4 Megacab Cummins