Though unlike BIll I've never seen the wall plate not put out power.... I've only worked on 2 RV's with this problem and both of 'em was bad cabling.
I DO know however it is possible for the light to be on.. the fuse to be good. and a DIFFERENT part of the wall plate assembly to go diodes up and not put out power.. I've seen that on so much other hardware.. So I support BILL's comment
OR he mine. take your pick we are in total agreement.
THe one thing many do not see is the roof conneciton. ON Some RV's it sticks up under a mountain of caulk. On mine it was buried under a cover and not visible. I knew it was there so I dug it out and replaced/repaired as needed (And as of 7:30 this AM it was working) (I'm watching DVRed tv now) . The other RV I worked on was a Sticks up under caulk kind. that one it was either the lower connection (which I was not willing to dig down to) or the wall cable. I got 'em TV by running a cable out the window to the antenna for their stay and when they headed out they stopped by a shop and they replaced the in-wall cable. ONly time I've ever heard of that cable going bad (And I've strung miles of coax over the years)