Before you rip out all of the fixtures, you may want to diagnose the one at hand. Hopefully you have a VOM meter so as to check voltage/polarity on the coach side. Hopefully all is well at the 12v source side of things.
Then you'll want to carefully look at the fixture. Try to see which wire on the fixture is attached to the center prong of the bulbs socket. That is to be the positive. After that, you need to discover if the coach wiring and the fixture are polarity correct. If so then the LED bulb is bassackwards and thats ok just as long as you know whats going on there.