Yes, it is interesting trying to figure out what goes to what.  Two things keep it interesting: FMC had its own logic for how they wired the coaches and then you get to try and figure out the logic of a PO (prior owner) or mechanic.

I presume that you have the wiring schematic for your coach.  That will at least give you the path for how the wiring started out when it left the factory.

In my case, since I am converting my coach to a Duramax, there is going to be major changes.  BUT, a new schematic will be drawn that will layout the new wiring scheme should anyone need it later.