I'll bet you didn't check ALL the fuses!! Heh heh. There is an undocumented fuse block under the dash, next to the steering column. I KNOW it controls my windshield fans, as well as my remote mirror.
If you are a contortionist, you might be able to see the block by lying on your back and sliding in under the dash... if not, use a mirror &/or take pictures with a digital camera. There is an ignition fuse located there.
My chassis is a Workhorse, gas.
Also, don't hold your breath trying to get circuit diagrams. And if you did (by some miracle), chances are this fuse won't be included because it is part of the original chassis wiring - at least on my coach.