The external jack is not intended for Satellite TV
The "indoor" end of that cable hooks to a bunch of electronics (The RF/Switch, amplifier power supply) and this is not allowed for Sat work, it very simply won't work unless you make modifications.
And it is usually RG-59, RG-59 is very lossy at Sat Frequencies, more than a few feet of it can be an issue.
My Recommendation is to install a new RG-6 line, labeled SAT on the outside (Either in a basement or via a bulkhead connector) and forget the existing cable line.. (Use it as designed)
Winegard's recommendations are as follows.
Inside the RV you have a wall plate (Or a box of many buttons, I'll cover the wall plate first)
It has a 12 volt outlet, Switch, LED, and antenna fitting.
REMOVE it from the wall, on the back there should be 2,3 or 4 coax cables,, With the 12 volt socket at the top, looking at the back the left one goes to the antenna on the roof.
The next one is the park cable line, DISCONNECT IT.
Connect the TV-OUT cable from the sat receiver in it's place.
Using a double female connector (What we call a Barrel conector due to it's shape) AND a short coax "jumper" extend the park cable to the LNB in on the Sat receiver,
(you may need to drill a hole for the cable, I recommend drilling it in the wall plate, Or better yet, "install" that barrel connector in the wall plate and label it "SAT" as well) then extend to the LNB in.
With teh switch off, it should work.
Box of many buttons.
On the back find the cable attached to the "CABLE" input on the box, Transfer it to the LNB in on the sat receiver.
But I still prefer to leave existing cables alone and install my own RG-6,, My receiver compartment is overhead, the RG-6 runs down the A pillar, under the dash, out thrhough the firewall (My rig is a gasser) to a ground block on the brake bell crank bracket under the hood, out of the weather and well protected.
Home is where I park it!