Professional towbar fitting, throughout Warwickshire and covering the Midlands

Towbar electrics explained

12N socketWhen buying a towbar for your vehicle for towing either a trailer or caravan, you will need to decide which type of electrical connection or wiring kit is required to attach your vehicle to the trailer or caravan. We can advise clearly and non-technically, either telephone 01926 512876 or drop an e-mail to

7 pin single socket, twin 7 pin sockets, (or the recent 13 pin socket).

The most common wiring socket is the 7pin single electrics connection, which will power the lights on a trailer or caravan.

Twin socketTwin 7 pin socket connections are used when a secondary charge is also needed, for instance if you are towing a caravan and wish to power a fridge or leisure battery during the journey then you would need this option rather than 7 pin.

13 pin electrics is the newest type of connection, whereby the single 13 pin socket has all the functionality of a twin socket connection, without the need to actually have two sockets. The 13 pin system has several advantages, including:

• New standard connection for caravans
• Future proof
13 pin socket• Twist and lock method of connection, removing the need to use force when connecting up your trailer, and making the connection more secure
• Just a single socket and plug needed, leaving a neater look and increased space around the tow bar

However one disadvantage is that due to the 7 pin and twin sockets still being very common, the situation is likely to arise whereby you need an adaptor for your 13 pin socket. These are easily available however and usually relatively cheap, and adaptors are available to fit any type of socket to any type of plug, for instance 13 pin socket to 7 pin plug, or twin socket to 13 pin plug.

Universal Electrics or Dedicated Electrics

Universal electrics has been the standard for many years, involving cutting and splicing wires into the vehicle’s existing wires to allow the power feeding from each wire to each vehicle light / function to also travel through to the corresponding trailer light / function.

Modern complex vehicle wiring and CANBUS systems now means that in many newer vehicles wires power more than one light and the power system often works on a pulse system rather than a constant feed. These changes have meant a bypass relay is required for most modern vehicles using universal wiring.

An alternative to Universal Electrics is Dedicated Electrics, also known as ‘Vehicle Specific’ wiring or ‘Plug-In’ electrics.

Dedicated kits are made specifically for each vehicle, and do not require the cutting or splicing of wires. Often a module can be found in the back of the vehicle in which the dedicated kit is plugged in, leaving a relatively simple job of feeding the wires through to a few points on the vehicle to connect in to place.

A Dedicated kit is more expensive and also does not usually come in the twin 7 pin socket variety however there are several benefits over universal electrics, please call 01926 512876 or send an e-mail to to discuss, we're happy to advise.

Bypass Relays

As car systems are getting more and more complicated, it is becoming vitally important to protect against faults and damage to the car system. For older vehicle models the towbar wiring works by connecting each wire from the tow bar socket to a point on the vehicle, and subsequently taking power from each point to power the trailer lights.

However many modern vehicles are using complex systems such as CANBUS or multiplexed systems. These systems work in a very different way to older systems and often involve wires powering more than just a single light. The power feed also usually works on a pulse system rather than a constant feed. These factors mean that traditional universal wiring is incompatible with the vehicles systems, and installing tow bar electrics can lead to a variety of problems, including:

• Trailer lights may work poorly or dimly lit due to insufficient power
• Trailer lights may flash in response to test pulses from the vehicle
• Vehicle fuse may be prone to blowing
• Vehicle may show a bulb-failure warning when the trailer is attached
• Vehicle wires may suffer from overheating
• Vehicle’s control systems may be compromised
• Vehicle central processing units (CPU’s) may be damaged

To ensure these problems do not arise, it is essential on modern vehicles to fit a bypass relay when using universal wiring. The relay basically fits between the towbar wiring and the vehicle wiring and prevents too much current being taken from the vehicle to the trailer, which is compensated for through a direct feed from the car battery. We always fit bypass relays when necessary.