Suspect list:
Bad cable or connector park (Confirmed good)
Bad cable park to RV. note. one common "Bad" is the center pin is cut too short.
Bad cable or connector INSIDE the RV (I have that)
Bad switch (The wall plate/booster or the box of many buttons).
Bad cable switch to TV
Best way to test
You need a cable and a double female (Barrel) connector or 2
One at a time sub your new cable for the existing
IE:
YOu did direct to TV so you know the new cable is good
Ok, now hook the new cable to the SWITCH. if you get a good photo you know the inlet to switch is the issue.
on my RV this is several lengths of cable with couplers (Barrel connectors) so I have the choice of running a whole new run or finding each connector and subbing for that run... I may go the single run route. Way better.. and I'll use RG-11 or RG-6 not that it matters that much but the cost difference is almost non existant and the quality .. much better.