Charlie-
My schematic shows no fuses, but there is one circuit breaker each for the mirror movement and the heater function. The movement power runs through circuit breaker CB5 in the electrical bay (driver's side front). Directly above the Ford-style solenoid are two bars of circuit breaker gangs, and CB5 is the fifth one down on the left bar, and is 15 amps. Check the connections for corrosion and tightness. The heavy wire coming into the solenoid underneath at its left connector should be the main positive feed supplying the electric bay panel from the 200 amp chassis fuse in the box above the batteries, so be careful. The two white wires at the outside of CB5 should be labeled as mirror wires, and likely go to the Velvac Mirror Controller, which should also be in the electrical bay; bundles of wires emanating from it go to the left mirror, right mirror, and your control switch on the driver's shifter panel.
If you have good voltage coming out of CB5, then you may have a poor ground at the Controller (green wire top of its left side) or a bad switch. But the wiring is complex, and it could be a number of things. I can email you the diagram(s) if you like.
Joel
