Towing Wiring for Caravans and Trailers

The information below is provided to assist you with connecting your caravan safely to your car.

The primary problem with all towing electrics is wear and corrosion.

The connections become worn over time and carefully cleaning the connectors will often help with many faults, such as bulbs not working etc. Also ensure that the pins which are split are not closed up by opening them back up gently with a small screwdriver. Do not over stretch them or they will break. The gap should be even for the length of the split.

A good sign of a problem here is blackness on the pins or loose pins where the plastic has partially meted. This is a sign that the pins are not making a good connection and are sparking and hence creating heat which will cause damage to your car and caravan.

If any burn or melting is apparant, the best advice is to replace the plug and the socket together to ensure you get the best connection.


Trailer Wiring Code

There are two general types of connection used by Caravans and Trailers to carry the essential signals from the towing vehicle to the trailer unit. The older units tend to use the 12N and 12S connectors, and the newer caravans and cars are now using the Euro 13 pin (ISO 11446) standard.

The 12N connector carries all the signals needed for a normal trailer (ie indicators, brakes, sidelights etc) and the 12S carries the optional signals for caravans (eg reverse lights, fridge supply, and battery charging).

The new 13 pin Euro Connector also referred to as the ISO11446 connector, ISO 4143-3 connector or the Jaeger connectorhas been in use since 2008 and is now the preferred method of connection.

The Wiring guides below are all based upon the standards, and should help if you need to reconnect new plugs and sockets, but if you have any doubts or questions, please contact your local qualified towbar specialist. If you get any electrical wiring wrong, you can easily create more problems than you had at the start.

12N Wiring Code

Pin Number Wire Colour Function
1 Yellow Left indicator
2 Blue Fog lights
3 White Earth
4 Green Right indicator
5 Brown Side light
6 Red Brake lights
7 Black Side light
12n Trailer Plug

The indicator circuits must have a warning light or sounder so that the driver knows when the indicators on the trailer are working.

12S Wiring Code, pre 1999 (British standardS)

Pin Number Wire Colour Function
1 Yellow Reversing light
2 Blue Battery Charging Via relay in car
3 White Common Return
4 Green Power feed for internal 12v equipment (not fridge)
5 Brown Spare
6 Red Refrigerator (via relay in car)
7 Black Spare
12s Trailer Plug

The auxiliary battery charger and refrigerator must be fed via a relay to prevent the vehicle battery from being discharged.

12S Wiring Code, post 1999 (European standardS)

Pin Number Wire Colour Function
1 Yellow Reversing light
2 Blue Spare
3 White Return for circuits connected to Pin 4
4 Green Power feed for internal 12v equipment or to charge caravan battery via a relay in the caravan (not fridge)
5 Brown Spare
6 Red Refrigerator (via relay in car)
7 Black Return for circuit connected to Pin 6
12s Trailer Plug

Important. The earth returns must not be connected together each must be run separately back to the car body earth.

The 12s socket must be wired in a minimum of 2.5mm² cable, throughout the cables length.

Euro 13 Pin Connector (ISO 11446 Standard)

Pin Number Wire Colour Function
1 Yellow Left hand indicator
2 Blue Rear fog light
3 White Common return for Pins 1,2 and 4-8
4 Green Right hand indicator
5 Brown Right hand rear position and end outside light and rear registration plate
6 Red Stop lights
7 Black Left hand rear position and end outline light and rear registration plate
8 Pink Reversing light
9 Orange Continuous power supply
10 Grey Power supply controlled by ignition
11 White/Black Common return for Pins 10
12 No allocation Spare
13 White/Green Common return for Pin 9
Euro 13pin Trailer Plug


Please Note: These wiring codes have been prepared with the greatest care and as far a we are aware they are correct however the British Caravanners Club and it's representatives cannot be held responsible for incidents arising from using these wiring codes. If you are unsure about anything please contact an approved caravan service centre.