I see you have a 9 way umbilical plug.... You have 2 conductors there which might be used. The fridge and the teletector circuit. The teletector is an antique flat tire warning system... Basically lights a light on a little box on the dash indicating a low or flat tire. This is a rare feature. It is very simple but works. If your teletector tubes are present and working, you might as well use it. Second is the fridge circuit. This is simply a charge line from your tow vehicle. In my opinion, this is just a big battery killer. If you have a drive which is capable of running on LP go that route.... No hi draw appliance to kill your tow vehicle batteries.
With the 9 pin connector you'll have to wire on on your tow vehicle as well, none come standard with one.
Best of luck. Remember heavier awg wire allows more electrical flow therefore more power where you need it most. Always use fuses or breakers, and lable every change both for yourself and future owners!