What is a 7 pin plug?
A 7 pin plug is used on such items as your bike carrier, trailer, boat trailer or horsebox. This plug only provides light functions and is connected to your car via the 7 pin socket on the tow bar. If your trailer does not have a fog light on it this may need to be retrofitted or not cut off from the vehicle.
There are no power functions with a 7 pin plug or socket.
It may be that your car has a 13 pin socket while your trailer, caravan, boat trailer or horsebox has a 7 pin plug. You can buy an adaptor to solve this problem. Older caravans sometimes still have 2 x 7 pin plugs. Newer caravans since 2008 will have a 13 pin plug.