Cable TV in connector in wet bay goes to a plate inside the RV where you can switch between the roof top antenna and the cable connector. In my 2015 Vista 27N that plate is in the compartment above the passenger seat on the right wall. That plate has a small push button switch and a small LED. Push the button so the LED is lit to watch from the roof top antenna. Push so LED is not lit and the TVs get connected to the cable TV in jack on the plate in the wet bay.
Either way you have to use the remotes on your TVs to go into setup menu to update the scan of the channels before you can watch anything after you have connected to cable TV and set the pushbutton the right way. Have fun with your new 27N. It's a great RV.
Randy - Manhattan, Kansas
2015 Vista 27N
2016 Honda HR-V