1989 Fleetwood Prowler. What is this power switch/box?

Jarata, that was me that made copies of my manuals and uploaded them. I don't see this switchbox in the electrical schematics.

Budwich, thanks for the advice. I will be getting to the furnace in a week or two. For now, I am focused on finishing the bedroom renovation (including "power center" remodel/upgrades)...so it would be great for now just to know what this switched wire goes to. :)