On the diagrams I attached previously, the second image, your culprit is the connection at J2 of Module A (10 CHANNEL OUTPUT MODULE DIMMER A), Jim. Intellitiec manufactures these Multiplex Output Data (MOD) modules, and it sounds like you'll need a new one. J2 on both modules A and B have only a white-striped brown and a red-striped yellow wire, tagged "MOD Data"; they are + and - data wires from the multiplex control, regardless, which splice to each multiplex switch throughout the coach.
As I understand Multiplex, and that's not very clearly, lighting is digitally managed - data sent to the controller on the above mentioned wires changes depending on how long a switch button is held, etc., and the two modules adjust dimming power to their respective lamps accordingly. The odd men out here are the two ceiling fans and the water pump, but they are on Module B. I would think the data circuit itself would use minimal amps, as opposed to the 10 amp lighting circuits they control, so it befuddles me (easily done) why your J2 connection would overheat. The multiplex controller itself I think is the "IPX CONTROL" in the diagram, and you can see it has its own red 10 amp fuse, which may be the one in position 9 on the inset 12v. house fuse block. Ed or Steve may understand this circuitry better, and can infer more from the diagrams and what you and I have written.
Before installing a new module A, I'd sure find out what caused the meltdown and why that controller fuse didn't blow to protect the data circuit. Did any of the switches get wet somehow? I know if I was anywhere near Bend I'd get in to have things analyzed by knowledgeable techs.
-Joel
click on the photo to enlarge it.
J2 is the white connector, nearest the fire extinguisher, on the circuitboard of Module A; they splice to the control, Com + and -, with the red wire supplying backlight power to the switches
