At that vintage, it's unlikely that such is available anywhere. But if you state your problem here (perhaps with pertinent pictures) there are folks here who can often help you troubleshoot very effectively. Maybe someone would even have a similar rig and supply pix or thoughts.
Very few RV builders evern make an actual schematic available but some do share the layout diagram for the unit's wire harness. Most do not have color codes for the wires as they just use whatever happens to be available. I would be very surprised to find any such drawings for an RV of that vintage. If you share what it is that you are trying to trace out someone here might well be able to help.