Wiring diagram for a 12S tow bar socket and plug

The 12S connector on your car provides power to the caravans reversing lights, interior lights, battery charger and fridge. The 12S socket is not always fitted to a car as if the car is just being used to tow a trailer only the 12N socket is fitted. The12S socket is supplied by a seven core cable with grey sheathing.

If you are installing a towbar yourself, need to check that the electrical sockets on your tow bar or caravan are wired up correctly then this page should help you check everything works ok and is wired up correctly. You will also find this helpful if you find that your 12S socket or plug has been damaged and needs replacing.

You can buy a replacement 12s socket or a 12s plug for just a few pounds, doing the job yourself will save you money compared to aksing your caravan dealer or local garage to do the work.

12n wiring colours Pin Colour What it does
1 Yellow Reversing light on the rear of the caravan
2 Blue Spare / +ve ignition
3 White -ve for the lights and charging the caravan battery
4 Green Caravan's interior lights and is connected to the car battery +ve
5 Brown Reversing lights or spare
6 Red Caravan Fridge +ve - only on when the vehicle is running
7 Black Caravan Fridge - ve


When connecting up a new socket or plug ensure that the wires are in good condition. Often, over time, moisture will get in the plugs and sockets and cause corrosion on the wires. These can cause poor connections resulting in the connected devices not working at all or not how you would expect.

Its important that you independantly wire Pins 3 & 7 to the car. This increases the wire load capacity and prevents overheating.