Your coach has an American Technology multiplex power controller under the bed. I'm guessing that's the circuit board you are talking about, the one that has two large power inputs and a bunch of fuses and relays. The board services the various digital switches around the coach, including water pump, interior lights, water heater, etc. The multiplex board itself receives operating power from a separate, small 12v wire that runs direct to the house battery positive post. It has an inline fuse, around 5A if I remember. If that wire is disconnected or the fuse blown, none of the circuits on that board will switch. Look for the wire in the battery bay.
Former owner of 2004 American Tradition and several other RVs
Home is in the Ocala Nat'l Forest near Ocala, FL