Windshield Wipers and Jake breaks don't work

So, my uncle recently bought a 2001 RD688S Mack Dump Truck, and the wipers and jake breaks don't work. I haven't looked over the truck extensively (I've done some minor mechanical and electrical work, but never on a big rig), but we're assuming electrical issues; maybe even fuses (and maybe the wiper motor/s). I've been unable to find any diagrams online for this truck, and my uncle has yet to purchase any kind of repair or maintenance manual. Can anyone here give me an idea of what to look for in order to get the wipers and jake breaks working (or steer me in the direction of a website that makes such information available, or offers diagrams... like, even fuse diagrams)? I'll mention that I have no idea how Jake brakes work, and only vaguely understand what they do (they're for slowing down on a slope?), so it may not be something that I can easily fix (unless it is just a fuse). The wipers, on the otherhand, should be an easy fix, if I could find any relevant information about the fusing, wiring and motor or motors. I really just wanted a few assembly/wiring/fuse diagrams to point me in the right direction, but I can't seem to find any (which seems unusual, as I've found similar diagrams for tractors, atvs, and cars/trucks in the past).