It is up to the convertor which way he wires up the Fridge/Freezer. Some are connected to the service battery for the ignition, but mine for example uses thr liesure battery. The main 12 volts supply for Fridge or Freezer comes from the fuse marked * and would not be used for the ignition circuit.
I have got one of these newish super dooper full size ff that selects the most efficient power sourse at any given time.
Or that is what the book says!
Our F/F (Reefer in US terms) has never gone out when travelling. Only when it has run out of gas.
Ralph - the cable from the step fuse is terminated behind te control panel above kitchen. If you do not have an ouside light, you wil also find in there a cable that can be used t power outside light so the switch on control panel makes it work.
I notice you still have the same M/Home as me. (Guessing you are the same Ralph I chatted to a couple of years ago)
If you need a copy of the Nordelettronica diagrams, I have somewhere on my computer and can email you them.