Tow Bar Electrics – A Beginners Guide

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Tow bar electrics are one of the most complicated parts of setting up your vehicle to tow.

You may think that you do not need to know the details as the company that is fitting your toe ball will sort all of this out for you 

However, if you don’t understand the basics, then you may find it difficult in the future to diagnose any issues that you may have and you may find that things won’t work correctly or in the way that you hoped 

In this guide, I will provide you with the most basic explanation of towbar electrics that I can. 

This guide is not designed to enable you to fit your own towbar electrics, but to give you an understanding and help you to correctly instruct your local towbar Fitter, and to help you to diagnose electrical problems

I have, however, included in this diagrams and tow bar wiring colors just in case a wire becomes loose or to help you diagnose an issue

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Tow Bar Electrics – Sockets Types 

You may notice that some vehicles have one socket next to the turbo and other vehicles, have two sockets one either side 

So what do the sockets to do? 

You may have heard the term 12 N and 12 S

What are 12N and 12S in tow bar electrics?

12N you may remember as N= ‘normal’ and 12 S as S= ‘ supplementary’

  • 12N – this powers all of the basic requirements for towing such as a indicators, fog, lights, tail lights, and brake lights
  • 12S – this powers additional electrics, such as reverse lamps, power supply in the fridge.

Vehicles with two sockets as described above have the ‘normal’ items for lights, etc. in one socket and the ’supplementary’ items in the other.  These are both seven pin sockets.

All vehicles (usually more modern vehicles) have now condensed the two 7 pin socket into one 13 pin socket.

12n-Tow-Bar-Electrics-Socket-300x167.jpg 12s-tow-bar-electrics-socket-300x165.jpg

If your caravan has one 13 pin connector, but your car has two 7 pin sockets then you can buy a conversion adapter as seen below.

Voilamart 13 Pin -7pin N and S Adaptor Lead, Towbar Electric Conversion Adapter Lead -Twin 7 pin,Euro Adapter Lead for Trailer Truck Caravan
  • 【European Standard】The small trailer plug simply plugs into the 13-pole plug Euro Standard Style plug and fits the other side into the 7-pin plug on most caravans / trailers.Notice: Black is the normal version which is for EU system(standard); gray is the special version which is for original UK system(standard ).
  • 【13 pin--7pin】1x trailer adapter 13-pin male - 12N and 12S 7-pin female.13 Pin to 7 Pin conversion,connecting a car and a trailer/caravan and supply power to the trailer/caravan for all important indicators, signal light and fridge. Make vehicle and caravan/trailer electrics compatible when towing.
  • 【Twin 7 Pin Electrics】7 pin 12N electrics provide legal lighting which includes brake, indicator and fog lights.7 pin 12S electrics provide supplemental lighting such as reverse lights, interior lights and appliances.N+S plug to ensure correct connection, and make it easy to get all your electrics up and running.
  • 【Easy To Install】Plug and play desig, without cable is used to connect the lights from the vehicle to the trailer with ease.Plug and play design, plug insert into socket, twist and lock, no need to change any cable.Insulated environmental PVC wires, waterproof performance.
  • 【Security】Locking springs Flap protects the connections when the article is not in use and locks into the 7 poles plug when in use.It also has an additional security that secures the attachment of the trailer to the adapter.Made of high quality nylon which has been given a mat-finish, providing a unique design and delicate feel.


Tow bar wiring kit

There are two types of wiring kit.  A vehicle specific wiring kit and a universal wiring kit.

Vehicle specific wiring kit

This wiring kits is dedicated to your specific vehicle and is usually the best option when ordering your tow bar.

To further complicate the issue, you have a further two choices to make.

You may choose a lights, only vehicle specific wiring kit, or a fully function, vehicle specific wiring kit.  For caravans I would suggest the fully function kit.  The alternative lights only wiring kits is better suited to people who only want to use their Tow bar for a bicycle rack.

Vehicle specific wiring kits usually need a dealer to programme the tow bar to the vehicle.  The dealer usually charges between £70 and £150.00 for this towing software download. (prices correct at time of publishing)

Universal wiring kit

If you choose a universal wiring kit, then this may not allow the vehicle to correctly communicate with your Caravan.  

Should you choose a universal wiring kit then you will also be faced with the dilemma of choosing a relay so that your caravan doesn’t drain the battery on your vehicle.  These two relays are known as a split charge, relay or a bypass relay.

What is a split charge really

The split charge relay will allow a permanent connection of electrics to your Caravan full lights (12N) but will only connect the electrics for the supplementary items (12s) such as the fridge when the vehicles output is above a certain voltage.  This means that your caravans fridge will not drain the battery whilst you are in the motorway service station having a coffee.

What is a bypass really

A boy pass relay effectively confuses the car, hiding the fact that it is towing a Caravan at all.  This is a bad thing.  You may only want to use a universal electrics kits with a bypass relay for bicycle, racks, or for towing a small trailer occasionally to the local tip.

Tow Bar Electrics – Conclusion

Navigating the roadways with your caravan or trailer in tow requires more than just a keen sense of direction; it demands a foundational understanding of tow bar electrics to ensure a smooth and safe journey.

🔌 Sockets (12N and 12S or the consolidated 13-pin): Your first checkpoint in assuring that your lighting and auxiliary functions, like that all-important caravan fridge, are in operational order.

🔗 Wiring Kits (Vehicle-specific vs. Universal): A critical decision point that ensures your vehicle communicates effectively with your towed companion, maintaining both safety and performance.

Relays (Split Charge & Bypass): Silent guardians of your vehicle’s battery, ensuring that power is judiciously used and safeguarded against unwanted drainage during your stops.

In the realm of tow bar electrics, your choices significantly impact the functionality and reliability of your towing setup. Whether you are sauntering along the coast with your caravan or making a quick run with a trailer, the backbone of a worry-free trip lies in the solid understanding and application of your tow bar electrics.

May your journeys be smooth, your choices be electrically sound, and your adventures always bring you back home, safely and satisfyingly. Here’s to smart choices, safe travels, and of course, consistently chilled refreshments along the way! 

Towbar electrics issues

Caravan For fridge not working on 12 V

If your caravan, the fridge isn’t working, when hooked to the towing vehicle, they may be several reasons why.

  1. Your engine needs to be turned on or the split charge relay will prevent power to the fridge.
  2. Check the red wire in the 12S 7 pin socket or the grey wire in a 13 pin socket as it may have corroded or become loose.
  3. Make sure that you have selected 12v on the fridge.

My rear lights are dimming when I indicate?

This is likely to be a problem with the earth on your car.  I had this issue myself.  Most cars these days don’t have a chassis so attaching the Earth to the body of the car isn’t always successful.  My only issue was resolved by running a Cable back to the battery instead of to the body of the car. 

Glossary of Tow Bar Electrics Terms

  • Single Electrics (12N)
    • Definition: A type of electrical system that powers the basic lighting functions on a trailer, such as brake lights, indicators, and tail lights.
    • Usage: Often used for bike racks and small trailers.
  • Double/Twin Electrics (12N and 12S)
    • Definition: A dual electrical system that provides power for both basic lighting and auxiliary functions in a caravan or trailer, such as charging the battery or powering internal appliances.
    • Usage: Typically utilized for caravans and larger trailers.
  • 13-Pin Electrics
    • Definition: A single plug system that combines the functions of 12N and 12S connectors, often used for modern caravans to supply power to both basic lighting and auxiliary systems.
    • Usage: Commonly used in Europe and becoming standard in the UK, ensuring compatibility across various locations.
  • 7-Pin Connector
    • Definition: An electrical connector with seven pins, typically used to link basic lighting systems between the towing vehicle and trailer.
    • Usage: Frequently used for utility trailers, bike racks, and other light-duty towing applications.
  • Converter/Adapter
    • Definition: A device that allows compatibility between different electrical systems, such as converting a 13-pin vehicle outlet to a 7-pin trailer connector.
    • Usage: Used when the vehicle and trailer have different electrical connectors.
  • Bypass Relay
    • Definition: A device that protects the vehicle’s electrical systems by preventing overloads when additional lighting and electronic systems are powered on the trailer.
    • Usage: Especially important in vehicles with complex or multiplexed electrical systems.
  • Split Charge Relay
    • Definition: A relay that allows the caravan’s leisure battery to be charged from the towing vehicle while preventing draining the vehicle’s own battery.
    • Usage: Primarily used in caravans and motorhomes to maintain charge levels in leisure batteries.
  • Towbar Wiring Kit
    • Definition: A kit that includes all necessary wires, connectors, and often relays needed to install tow bar electrics.
    • Usage: Essential during the installation of a tow bar to ensure safe and legal towing.
  • Dedicated Wiring Kit
    • Definition: A vehicle-specific wiring kit that integrates with the vehicle’s existing electrical systems without altering the vehicle’s electrics.
    • Usage: Often preferred for modern vehicles to ensure seamless integration and preserve the vehicle’s warranty.
  • Universal Wiring Kit
    • Definition: A general wiring kit that can be used across various vehicle models and brands but does not integrate with vehicle-specific electrical systems.
    • Usage: Sometimes chosen for older vehicles or where dedicated kits are unavailable or cost-prohibitive.
  • Socket (or Trailer Socket)
    • Definition: The component mounted on the tow bar into which the trailer’s electrical plug connects, ensuring power is supplied to the trailer.
    • Usage: Used in all towing setups to ensure electrical continuity between the vehicle and trailer.
  • Electrical Circuit
    • Definition: A complete, closed path through which electric current flows from the power source to the device and back.
    • Usage: In tow bar electrics, circuits ensure the correct flow of electrical power to various trailer functions.


It’s imperative to ensure that tow bar electrics are installed and functioning correctly to maintain safety and legality on the road. Furthermore, compatibility between the towing vehicle and trailer or caravan must be checked to avoid issues while on the move.



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