7 Pin Plug are used for road lighting only.
This is currently the most popular plug used for towing as it does the lighting on most trailers and caravans.
This is slowly being replaced by the European 13 pin plug and will become less popular as the reverse light is introduced to new trailers between now and 2012 when it will be legal requirement.
All trailer plugs and sockets are very simple to wire.
To wire a plug or socket the first thing to do is to disassemble the plug or socket, this is very simple as the centre part that the wires fasten into can then be removed giving easy access to the screws then fasten the wires to the relevant pins.
All pins are marked and it can only be assembled one way.
- 12 Volt