Cable from factory installed winegard dish

Run a continuity check. Hook an extension coax to one cable, take the other end of the extension through a window up to the dish, unhook the coax from the dish, use a multimeter on "ohms" setting and put a lead on the center wire at each open end of the coax. Do this until you get one that has zero resistance - that's the one you want. Then label it down below.

Its very simple,....chop the end w/ plug (4") off an old coax cable. Bare the end 1" back and twist the center lead and braid together. Its then called a "shorted coax cable":) Then connect it to either end of one of your 3 cables using a barrel connector. Go to the other end and check for continuity.
Note, all 3 cables must be unplugged on both ends, (show no continuity) before you can do this.
Or I'd guess you could eliminate the 2 cables that aren't connected to the dish.

What kind of Winegard antenna?

Well, there's always the trial and error method. Plug one in and see if it works...if not go to another....and then the third. I mean really... you're right...how hard can it be?

Ron

Dealer is 2 hrs away.... Thought "gee how ared could this be?" There goes tha

if you have a new rv I'd go to the dealer and have them deal with this issue. you have a 2015.