This is the comment on Ryder towing website
* On caravans post 1996 this feed is automatically switched during towing by a relay in the caravan to charge the caravan battery. When this happens, other interior circuits are off (except fridge).
Hi Avril,
Having looked it up I think it was 1998 so applied to 1999 vans onwards.
Since then the 12s should be as follows:
A feed to operate the caravan's reversing lights (if fitted) via Pin 1
A 12-volt supply from the car battery via Pin 4 all the time your car is hitched up.
A feed via Pin 6 to operate a fridge while the engine is running.
A feed to charge the caravan's battery, which is only activated when the engine is running. This was previously via Pin 2 but charging will now operate via Pin 4.
An earth connection. This was previously via Pin 3 alone but is now to be accompanied by another earth wire via Pin 7, exclusively for the fridge.
So the relay you refer to is in a different curcuit to teh fridge, the Fridge has its own direct feed, switched by a relay in the car so it cannot drain the car battery when the engine is not running.
Hope this helps.
Alan