Finding a schematic for this old of trailer might be next to impossible. If you are taking the inside skins down, I would replace all of the wiring and make your own schematic.
That way you are sure of two things-you have upgraded wiring and you know where everything goes along with having an accurate drawing.
This is what I did with mine.
WBCCI# 9259 AIR# 38927 TAC-TX 14
Stop Littering-Spay & Neuter-- Adopt From Rescue
No amount of time will erase the memory of a great dog.