To my vague recollection, BCS once accessed part of our cover mechanism via a cover under the carpet, next to entry tile, beside the driver's seat.
But as to what your Monaco rep said about the cover being not air driven, ours is a 2006 powered via an air cylinder activated by an electric valve. As long as there's at least 60psi in the tanks, it will operate.
You might want to diassemble the other switch and see if one of its leads is hot - this is some sort of two-way wiring setup. But it is more likely your power source is faulty. As Fred noted, your newer coach may have a Multiplex system in the chassis side; my 2006 model has Multiplex only in part of the house side. Rather than a fuse, there is a likely a circuit breaker in your electric bay, streetside front; but then again I'm not familiar with a chassis multiplex system, and leave it to others to speak to that.
Below is a combo-photo of the pertinent part of our legend for that bay and our coach manual. Breakers 15 & 16 (the left top, #two & three) are for the step itself, so ignore them. I'm not sure that breaker 37 (bottom left) is for the cover, but check its connection regardless; plus, your model may have breaker wiring quite different than mine of course. But perhaps the information will help in some way. Most coaches came with an electrical legend pasted on the inside of that bay door, but most legends seem to have also fallen off or faded.
If the cover was screw-drive, back when the cover did operate I'd think you'd have been able to hear the motor such a mechanism would require. Except for the slight friction of the sliding cover itself in its track, ours is otherwise whisper quiet.
Also, the cover can jam in its track such that it won't appear to respond either way, especially with a relatively noiseless air-drive system. But your lack of 12v. at the switch is telling another story. With coach and chassis main battery switches off, use your multimeter to check for continuity of at least one of the cover switch wires to ground.
Joel
(click on the text below the image to open it larger in your computer's photo program and copy it. I can email you a better image if you require one.)