Not sure what year your 351DS is, but we had all sort of issues with our coax cables. On ours, there is a manual switch box on the overhead passenger's side cabinet. Black box velcroed down with a selector switch.
Now, originally our antenna TV worked fine, but nothing else. Also one TV had perfect reception while the other didn't. We ended up having two problems. One was with the connectors not being crimped properly. The other was with the coax cables not being hooked up were they belonged. I had to remove the box and figure out which cable was which. You should have a cable that comes down from your antenna to the amp's receptacle (white receptacle with a coax input and a power push button for the amp). From there it should be routed to the back of the switch box marked antenna. Then one from the back of the amp's receptacle (aux) to the back of the box marked aux. The last input to the box should come all the way from the back end of the coach for your "cable". You then have one output from the switch box that feeds all your TVs.
Like I said, on ours the only one that was hooked up right was the antenna one, but nothing else worked. I bought a tool to figure out which was which and got them all sorted out. Now, we can switch the box to antenna or cable when needed and have perfect reception.
Good luck, and let us know how it goes.
2014 Georgetown 351DS
-TruCenter -Front/Rear CHF -Hellwig Links -Tiger Trak -Ran McNally GPS -ScanGauge -Truck Systems TPMS -5 Star Tune