There are actually three different tow bar electrics connections that you need to know about. Twin 7, Single 7, and 13 pin.
Let’s start with the 7-pin connector.
The 7-pin tow bar electrics connector will give you the basic lighting functions you need when carrying or towing anything with the tow bar. These functions include the brake lights, the side lights, the indicators, and the fog light. They do not include reverse lights.
Twin 7 pin wiring
Although only used on older trailers and caravans the twin 7 wiring consists of the vehicle lighting functions plus auxiliary power for ATS stabilisers, auxiliary battery, and fridge.
The twin 7 pin wiring is made up of two sockets/plugs. One is the 7 pin connection and another plug, normally grey in colour, that has wiring for auxiliary power and reverse light,
13 pin Towbar Wiring