Towbar Electrics

Towbar electrics have changed considerably over recent years. The electrical systems of the modern car have changed so much that these are not now suitable for DIY fitting. No longer is it just a case of joining into the rear lamp circuits. Modern cars have a maximum current draw of 10 milliamps from the lighting circuits. Cars almost always have bulb monitoring systems that can be affected by incorrect towbar wiring. We at TrailerTREK are experienced electrical installers and have the knowledge how to utilise the vehicle electrics utilising CANBUS systems.

No longer is installing your towbar easy to do as manufacturers are increasingly making more complicated electrical systems. TrailerTREK towbar fitters keep up to date with manufacturer products meaning that you the customer get exceptional service and reliability.

Towbar installations often means the removal of bumpers and some towbars involve a neat bumper cut which our installers are professionally trained to do safely and without compromising the looks of your vehicle.

Universal Electrics

When installing universal wiring systems we include the cost of the buzzer or bypass relay, sockets and cable etc. in our quotes making it by far the most cost effective solution. Our TrailerTREK installers carefully wire electrics into your cars circuits using sophisticated full logic bypass relays to protect all of your cars systems and to independently power your trailer lights without drawing large currents from your cars lighting circuits.

There are 4 main types of relays used:

A Buzzer - This is used mainly on older cars when no bypass relay is needed but an audible indicator warning is still required.

A 7 Way Full Logic Bypass Relay - This is used on most modern cars with bulb failure systems, multiplex lighting limited current draw circuits.

CANBUS Relay - This is a universal version of a dedicated kit, it self dedicates and can be used with cars with CANBUS and TSP and has a built in combi relay.

Combi Relay - This is a split charge relay used to protect the cars battery from drain and switches on caravan charging and fridge on when the car is charging enough. This is only used with 12s (grey) or 13 pin sockets.


There is often speculation as to which type of connection is best. The truth is they all have their place depending on the application. TrailerTREK Towbar installers are trained to utilise any of these techniques although some are more time consuming.

Crimp Connections

Crimp Connections are an effective join that can have good insulating qualities but should always be checked by pulling after each crimp. The drawbacks are that they can be pulled out with force or if poorly crimped, but are very good for removable joints. If joined to a wiring loom the loom will have to be cut. These are best used on ends of wires, to join identically sized wires or to join in something that can be removed if needed.

Soldered Connections

Soldered connections are often favoured as they are very strong and won’t normally pull out. A proper soldered join should be insulated and air tight, normally by using a heat shrink sleeve (pvc insulating tape is not sufficient).

Displacement Connections

Displacement connections are the only join to not cut the original wire. They join by using a blade of metal that displaces the insulation around the copper wire and makes a connection bridge between the copper wire of one cable to that of another. These come in a variety of different sizes and it is important that the correct size is used to avoid bad connections or damage to the wire.

Universal Bypass Relay’s

Smart Universal Can Bus Module

The Smart universal canbus module interfaces directly to the vehicles Can Bus. It recognises the host and self dedicates to that vehicle and sends data back to the car about the connected trailer. This enables towing related functions such as Trailer Stability Programs and normally has a built in Caravan function. This system offers an alternative to a dedicated wiring kit.

Ultra Smart Bypass Relay

7 lamp bypass with programmed microchip controller, intelligent switching on all circuits makes the trailer lights work correctly at all times, however complex the car's lighting control system.

The advanced relay uses logic to control the switching of the trailer lighting circuits. The ultra smart bypass, with its enhanced logic will work without adjustment on virtually all current 12v cars. It bypasses any vehicle bulb failure warning systems.

Flasher Circuit Buzzer

Rear flasher buzzer: a legal requirement, and a useful reminder when you are about to turn a corner that you are towing. Joins to both indicator circuits separately.

Combination Relay

Used with twin sockets or a 13 pin socket for caravan towers. This relay provides charging power to the caravan's leisure battery and to the caravan's fridge when the vehicle engine is running and the vehicles alternator provides enough charge. The relay stops the caravan from drawing any power and flattening the car battery if there is not enough output or the vehicle is not running.

Dedicated Electrics

A dedicated towbar electrics kit is a wiring kit designed to fit and integrate specifically with a given make and model of vehicle. It does not necessarily mean that it is the manufacturers original equipment wiring kit. Being dedicated as opposed to universal means that it will not fit another vehicle other than the one or ones it is specifically designed for. Sometimes an electric kit supplied by the manufacturer will be a universal kit rather than a dedicated kit, depending on the requirements of the vehicle.

The sophistication of a dedicated electrics kit can vary from that of a simple buzzer universal wiring connection, a bypass relay universal kit, or a more complex CAN BUS module integrated system. For this reason the costs of these kits can also vary considerably. The added functionality of using a dedicated kit over a universally wired kit may be nothing at all. However if your car has added functionality from using a dedicated kit, such as a Trailer Stability System then it may be worth the extra investment. We can advise you on this should you wish to purchase dedicated electrics.

Most dedicated kits need the cars ECU recoding to activate its functions. An additional cost from dealers can result due to the cost of the diagnostic tool used to reprogramme the cars circuit board.