Re: Red Hot Fuse Relay.
Gonzo, since by your own admission you do not know much about electrics, you need professional help with this right away -- before the bus catches fire. Might want to disconnect the batteries in the meantime.
Just one "do it yourself" question for you: Does this dramatic overheating of a component by any chance happen only when you start the engine, and then it cools off again? If so, then you would have no ground from the starter back to the battery, and the starter current would be returning thru any conductive path it can find. You can investigate this by connecting jumper cables from the engine block to the battery negative terminal. If the "red hot" problem goes away, then an engine-to-battery ground strap has failed. But I hesitate to tell you to perform this test... until we are resonably certain the bus is not about to catch fire.