Rich,
My NRV is older but, has the florescent lights and step light switch. In addition, it also has a rocker switch on the fixture itself. Someone turned it off there one time and the step switch didn't work. Took me awhile on that one
Unless your 12V system is protected by breakers (which I doubt) the 12V fuse panel should be located close to the converter/charger or inverter/charger if so equipped. It doesn't sound like it's a fuse though if the 1 light is the only thing not working.
When checking the switch for power, use a few alternate grounds for testing if possible as it could be a bad ground there (not likely, just being thorough). You of course want to check for power into the switch as well as out to make sure the switch isn't bad. You could have power at the switch and at the light too, but the ground up at the fixture could be bad. (happened to me once and had to install a new ground wire). Since there wasn't an alternate ground close enough for me to use, I used a 12v battery charger and connected directly to the wires after any switches....lit right up.
If your meter will reach the fixture and the front AC panel, you could use a ground there as an alternate to test. You'll probably have to get DW to hold one wire though
If you're 100% sure there is not power at the switch (and you checked for that fixture switch I mentioned earlier), then the problem is certainly between the switch and the fuse someplace. I don't know if this will help you, but it will keep you busy for an hour or so if you think I'm on the right track. Good luck and keep us posted.
John...