The Different types of wiring avilable for a towbar
All these different wiring options which one do I go for ?
A towbar is not just the metal work that fits under the vehicle but there is another part to the fitment, that part are the electric‘s.
There is a lot of confusion to what type of electric‘s there is available for a towbar fitment and what you exactly need in order to make the lights work on the back of your trailer or caravan and also keep the vehicle electric‘s safe. This guide will cover this and hopefully throw some light on the subject.
The Standard Single Electric‘s - Or known as 12n
This is the standard single electric point that you see on most towbar fitments. This is made up on one 7 pin electrical socket which is either mounted next to the towball or tucked under the bumper on some towbars. The purpose of this socket is to provide your road running lights for your attachment or lighting board.
This is basically all you need legally to tow but it is a little restricted in the functions it will provide. There is a myth that you can not tow a caravan with a single electric point but this is not true. It will however restrict your options with towing caravans and will prevent working some of your caravan functions.
The single socket has the following feeds to make the lights work:
Pin 1 - Yellow - Left hand flasher Pin 2 - Blue - Fog Light Pin 3 - White - Earth Pin 4 - Green - Right Hand Flasher Pin 5 - Brown - Right Hand Tail Light Pin 6 - Red - Brake light Pin 7 - Black - Left Hand Tail Light
In the single socket there is no feed for the Reverse light, this is in the Second Socket (12s). Reverse light working is not a legal requirement.
UK law states that there must be a warning to tell the user that the indicators work on the trailer while towing. This is only applicable to passenger vehicles in the UK, in different areas of the EU this may differ, This can be a audible or visual devise. We supply a audible buzzer which is mounted in the rear of the vehicle and sounds with the indicators only when towing. If there is a bulb blown on the indicators of the trailer then the buzzer will not sound. We find this the best wire as most of the wiring is then done in the rear of the vehicle.
You can either then find the vehicle wiring colour coding from the person you purchase the towbar from (This is a service we offer for most vehicles) or use a tester to discover them yourself.
This is normally connected using scotch lock connectors piggy backing off the existing loom in the vehicle. For a lot of early vehicles this is OK but a lot of the modern vehicles from 2002 onwards you can not do this as it could cause a effect on the vehicles electrical system for the following reasons
Some of the modern cars have bulb checking which informs the driver of any bulbs that do not work.
Some vehicles have a pulsing system on the wiring to check the vehicles electric system. Wiring straight into this would cause the lighting board wires to pulse.
Some vehicles have a low voltage system which would not power the trailer lamps
Some vehicles tail lights take over from the vehicles brake lights in a bulb failure which causes problems on the trailers wiring.
Some vehicles have a stability program which normally informs the vehicle that it is towing when the single electric‘s are plugged in with the manufactures genuine wiring kit but with using just a standard after-market wiring kit it does not inform the vehicle.
Not to be put off by these points there is a simple solution and this is done by relays.
The most advanced relay we supply and use is the Smart 7 way bypass relay. This is a small box which lies in-between the car wiring and the trailer wiring. It fools the vehicle to think there is nothing connected.
It is normally easily wired in with screw connectors to connect the relay to the trailer harness and another harness running from the relay which are the same colours as trailer wiring.
You then have to provide a fused main feed and a earth to this box and so long as you have selected the correct wires it should divert the power to power the lights on the trailer from the main feed and only use the vehicle’s wiring harness as trigger to tell the relay that different functions are operating and to divert the power from the battery to the trailer.
2 way bypass relays perform a similar function but only on two circuits normally only the tail and brake lights.
Do I need Twin electric‘s ?
Twin electric‘s or 12S as they are called is not needed to legally tow but will be prevent some things working inside your caravan.
A main permanent feed is needed either from the fuse box or the vehicles battery which means on many occasions you have to run a fused feed to the front of the vehicle.
It will add the following functionality in your vehicle, reversing light, fridge working, caravan battery charger working, caravan interior light working.
The pin configuration for the twin electric‘s is as follow
Pin 1 - Yellow - Reversing Lamps Pin 2 - Blue - Caravan Battery charging (Not connected after 1999) Pin 3 - White - Earth Pin 4 - Green - Perm supply powers caravan interior lights Pin 5 - Brown - Spare (Not used) Pin 6 - Red - Switch supply to refrigerators Pin 7 - Black - Earth
This works off the 12 volt battery in the car and is meant to maintain the battery level and the fridge temperature. It will not cool the fridge down from it being hot for example.
The Switched feed for the caravan battery and the fridge is controlled by a number of ways.
Voltage Sensitive relay which will only trigger at 13.5 volts (When the vehicle is running) and feed the battery charger and fridge. When the engine is turned off the voltage will drop below 13.5 volts and this will cut the feed to these devices. We supply full twin electric‘s with relays with all our twin. Most companies only sell
Ignition relays work when the vehicles ignition is turned on and this triggers the fridge and battery charger to work. When the key is turned off then the power is cut.
Twin electric‘s are ideal if you have long journeys or you like to camp in fields with no caravan services.
13 Pin Electric‘s
This is the continental style electrical connection. Both the 12n and the 12s electric‘s are contained within the socket which is about the same size as a UK trailer socket but contains 13 pins rather then 7 pins.
To connect instead of pushing in the plug you have to push in and turn to lock. This socket is used in mainland Europe and there has been a lot of talk of converting the UK to this method but no movement on this at the moment.
You can use this socket with UK 7 pin plugs which are on all UK trailers and caravans but you will need to use a convertor which will split the 13 pin electric‘s down to two 7 pin sockets or one single 7 pin socket depending on what you are towing.
This type of connection is ideal to use with a detachable towbar where there is only one space to mount one socket which sometimes can then be flipped out of view when not being used.
Plug In Electric‘s Kits.
These electric‘s have increased more over the last six months and can be obtained for the most popular towing vehicles. The main reason for the increase in popularity is due to the advancement of vehicles wiring as they are made to work in tune with the vehicles wiring structure integrating with any dashboard icons and cutting out any reserving sensor feeds when connected so they do not sound when towing.
These mostly plug into a dedicated trailer plug or into the back of the lamps of the vehicle, very rarely you will have to make connections directly to the harness.
Each kit for each vehicle works differently and some are plug and play but some need you to take the vehicle to the main dealer in order to tell the vehicles computer that there is a trailer plug in wiring kit attached.
There are many advantages to this system but the main disadvantage being the cost which can be over 10 times the standard universal wiring kit and the fact that most of these kit come only in 12n single electric‘s not the twin electric‘s.
This guide is written by towbarman01
Towbarman01 is the user name of Towequipe who has been selling and fitting towbars for over 35 years, and selling on ebay for over 5 years. They are a family company now run by the 2nd generation of the Rowson family and six members of the team our family members.