This is the most common and cheapest connector type currently used in the UK. It will fulfil all normal towing requirements under UK law and it can be used with lighting boards, cycle carriers, old caravans, garden trailers, plant trailers and horseboxes. In fact, almost anything you can connect to a towbar. A 7-pin electric kit will not power the inside of your caravan.
Lights on a caravan, trailer or cycle carrier (indicator, fog lights, brake lights).
Interior appliances of a caravan (fridge, caravan battery) Reverse lights (caravan, cycle carrier, trailer).