this photo you can see the electric cable that connects to the tow
car via a electric plug.
Most caravans come
with a 13 pin plug. You can still connect to your towing bracket even if
it is 7 pin type. All you need is an adapter.
If however you want the refrigerator to run on 12 volt while you drive,
and 12 volt to some of the lights, in the caravan during a short stop,
or while you are setting up the camper on the campsite, the the car need
a 13 pin plug also on your car. The water pump and the toilet flush is
also 12 V in most cases.
To prevent your
car battery to go flat, normally a relay is installed, so the
refrigerator is disconnected when the ignition key is off.