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Which Tow Bar Electrics are Best for My Car?

This is a more vital question than ever now and one of the most common questions we get asked at Trident Towing Kent.

Vehicle technology has almost completely changed in recent years and tow bar electrics have had to change as a result – going from universal relays to specialised, vehicle specific kits.



These are for older vehicles up to the late 1990s without computer systems and modern technology.

The traditional way of fitting tow bar electrics to these would be using a basic universal electrics kit such as this one.

The 7-pin socket is fitted to the tow bar, and if not already fitted, attach 7-core cable to it in the correct pins as per our electrics diagram:

Using a wiring tester tool, find the vehicle indicator wires on the car coming from the rear lights – to these, crimp in the indicator wires on a universal buzzer relay such as the one below.

The rest of the wires for the vehicle brake lights, fog light and side lights, would need to be found on the vehicle. The remaining relay wires and 7-core cable wires then get crimped to these wires. The white wire on the relay is the earth and would need to be attached to a metal part on the car using a ring terminal.



From the late 1990s, cars began to feature bulb failure warning systems, where an alert appears on the dashboard when a light bulb on the car fails.

This is the first complication in towing electrics. Using the same relay in the basic kit above would result in multiple dashboard warnings.

The relay takes voltage from the vehicle loom which is recognised and translated as a bulb failure by the vehicle system.

To get around this, a bypass relay is needed which takes its’ power from the vehicle battery or fusebox instead of directly from the loom.

This way only a minimal voltage drop is taken from the loom which the bulb failure warning systems will not recognise.

At Trident Towing you can order from us either just the bypass relay on its’ own, or as a complete fitting kit.



Vehicle Specific Kits are made for modern cars from the mid 2000s on, and especially ones made in the last 3 years so as not to affect your vehicle warranty.

With advances made in vehicle technology, the newest cars now have a huge range of electrical features compared to even only a few years ago, such as:

  • Adaptive lighting;
  • Re-generative braking;
  • Reversing cameras;
  • Stop/Start systems.

As part of this, vehicle manufacturers now incorporate towing functions into the vehicle electrics to increase safety and towing efficiency.

For example:

  • Trailer Stability Programs (TSP) can correct any trailer snaking in crosswinds;
  • Auto-levelling suspension compensates for the trailer weight at the rear of the vehicle;
  • Reverse sensors will automatically cut out so they don’t sound in reverse with a trailer on the back.

CAN Bus (“Controlled Area Network”) wiring in vehicles is a large part of what makes this possible. Instead of a traditional loom, a CAN bus uses a control unit for each set of functions on the vehicle.

This different method of vehicle wiring has made universal electrics kits redundant on new vehicles. Fitting a universal kit to a modern vehicle can result in the following:

  • The vehicle manufacturer can void the warranty on your new vehicle as universal electrics have not been approved for use on the vehicle and are not designed to work with the CAN bus systems;
  • The built in trailer towing functions will not be able to function without the Vehicle Specific Kit;
  • Other electrical functions, as well as safety and security systems on the vehicle can be compromised.

Fitting the vehicle specific towbar electrics means that:

  • The Vehicle Specific Kit (VSK) fits into provided connectors on the vehicle and communicate directly with its’ CAN bus system;
  • Because it is specifically made for the vehicle, only will it communicate with the car and activate any tow bar related functions;
  • It will also ensure that the other electrical functions on the car will not be affected.

In many cases a vehicle software update is needed in order to calibrate the new electrics to the vehicle. Here at Trident Towing we have all the latest diagnostic systems and incorporate vehicle coding free of charge into our already renowned tow bar fitting service.

We hope this helps you with some tow bar electrics queries. We will also be covering tow bar electrics for caravans in a future blog.

If you have any further queries in the meantime,please do not hesitate to contact us and thank you for choosing us at Trident Towing Kent.

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