Ok, Thinks I have seen:
Multiple Wall Plate/power inserter/Switches... Got to find the right one (Very rare)
Wall plate off/fuse blown
Wall plate not even connected
Bad connection (Roof pass through)
Bad coax
Missing head (ok you don't have that one)
Now I'm not a professional RV tech but twice it's been the roof pass through One was a pass through (it stuck up through the roof) I traced the problem to that point provided a bypass line and a dealer/shop fixed it (Tear into roof... NOT on your rig will I) The other time (my own) the connection was in the roof ( **THOUGHT** sealed (not very well) and had corroded to dust or darn close to it. A new barrel connector and two new waterproof compression cable ends and SUCCESS.
I've also seen popped fuses though on my rig I never found the @34#@ fuse for that circuit.
A test light is your friend by the way (Google automotive test light or visit most any auto store or departmetn, Looks like an old fashion ice pic)
Home was where I park it. but alas the.
2005 Damon Intruder 377 Alas declared a total loss
after a semi "nicked" it. Still have the radios
Kenwood TS-2000, ICOM ID-5100, ID-51A+2, ID-880 REF030C most times