My 1992 Bounder has developed electrical issues associated with the switch for the radio  from vehicle battery to house battery. I may need to replace the switch and also need a wiring diagram to see how it is wired. There is a fuse under the dash for the radio, but only is hot when key is on. (ignition or acc) I believe that this power source should be hot when either the key is on or the switch is to "Park".  

 Is there a parts supply  for this old bus somewhere?