Man are you in for a fun time . . .
First, follow the outside cable connection to wherever that takes you (probably somewhere in the basement on the door side).
It will go to a splitter somewhere near an outside TV coax hookup . . . this is where I found the very first problem as the outside cable connection was hooked up to one of the outputs on the splitter . . . not the input (splitters are one way - thus no signal), and the input of the splitter went to the outside TV hookup!.
That is how it came wired from the factory . . .
Next, check ALL of your coax connections and make sure they are tight, including ALL splitters.
And last but not least, if your Jensen stereo has the antenna hooked up to the roof antenna via coax to a splitter behind the stereo . . . unplug the radio antenna from the coax and buy a diapole or an outside mount antenna as this was shorting out the cable signal in our Prowler.
And this is just for starters . . .
Good luck!