We may be confused and maybe we are making it harder than needed?
It's likely one of those little things that we can look at and still not see it?
So maybe a picture of what and why it is hard to spot will help, whether motorized or trailer?
What you are searching for is the faceplate like an electrical outlet except with a coax connection and a tiny little button switch!
Click this for better view!
We are kind of guessing but I would expect to find this in a cabinet likely up front, maybe over the windshield on Motorhome?
The trick is the tiny little button that is almost hiding behind the finger! That needs to be on if using the antenna or off if using cable.
When it is on, there is often a light on the panel just under the roof antenna which lights. Once that indicator light is on, you can begin to adjust the antenna by turning or using the gain adjustment on that plate.
If it has indicator lights, get as many LED lit as possible as that indicates stronger signal!