Like Iggy said, check for shorts. You can take a multimeter, if you have one, to make sure there isn't any continuity between the center conductor and the outer conductor (braid). I had to repair a couple of ones in our brand new unit. I bought a pretty nice tool that you hook up the main unit to one end, and then remote terminators on the other ends and it will tell you the condition of the line along with where it goes. Got if from ebay pretty cheap and it solved all my cable headaches.
2014 Georgetown 351DS
-TruCenter -Front/Rear CHF -Hellwig Links -Tiger Trak -Ran McNally GPS -ScanGauge -Truck Systems TPMS -5 Star Tune