Tow bar electrics

Tow bar electrics explained

The complexity of modern cars means that fitting tow bar electrics can be very difficult. It is important to choose the right electrics to suit your towing needs, whether that be towing a caravan, trailer, cycle carrier or anything else.  

There are 3 types of towing electric sockets to choose from depending on your personal preference and towing needs, they are single 7 pin electrics (12N towing electrics), twin 7 pin electrics (a combination of 12N and 12S towing electrics) and single 13 pin electrics.

After you have chosen a type of towing electric socket you will need to decide on tow bar wiring kit, there are 2 types, universal wiring kits (fits all vehicles) and dedicated wiring kits (fits specifically to a single vehicle).

Then all you need to do is fit it to your vehicle.

Click here all FAQs about tow bar electrics.

Tow bar electrics sockets

Single 7 pin electrics

single 7 pin electricssingle 7 pin electrics

Pin locations are from rear of socket.

Single 7 pin electrics, also known as 12N towing electrics are needed to power the lighting on a trailer, caravan, cycle carrier or anything you're towing. (The single 7 pin electrics power left and right indicator and taillights, fog lights and brake lights.) If you don't require any further power to your towing counterpart, the single 7 pin electrics socket will be your main choice.

Twin 7 pin electrics

twin electricstwin electrics diagram

Pin locations are from rear of socket.

Twin electrics is a 2 plug system which combines the single 7 pin 12N electrics socket with a 12S electrics socket. You will need twin electrics if you require more power than what a single 7  pin socket can provide on a pre 2008 manufactured UK caravan (post 2008 UK caravans are fitted with 13 pin connectors). The twin electrics will power everything that a single electrics system powers plus reversing lamp, battery, power supply and fridge. The brown pin 5 in most cases is not used when wiring tow bar electrics and it is important to ensure that the white pin 3 cable is earthed.. In some cases a split charge relay might be needed in order for the power to switch divide from charging a leisure battery and the car battery.

13 pin electrics

13 pin electrics13 pin electrics diagram

Pin locations are from rear of socket.

13 pin towing electrics are the most modern style of towing socket, all EU caravans post 2008 will be fitted as standard with a 13 pin electrics connector. This is essentially a 2-in-1 socket, it has all the capabilities as twin electrics in one rather than 2 separate sockets. 13 pin towing are more adaptable for detachable tow bars that have a spring mounted single socket plate that can be folded up behind the bumper so that it's invisible.

Conversion leads are available for 13 pin towing electrics to twin 7 pin towing electrics or twin 7 pin to 13 pin towing electrics if your vehicle has a 13 pin socket and your caravan has twin 7 pin towing plugs or vice versa.

Wiring kits

Once you have chosen which electrical socket you need, you can choose which wiring kit to fit.

There are 2 types of wiring kits to choose from, dedicated and universal. Universal kits are available for all vehicles whereas dedicated are vehicle specific so may not be available for some cars (more information on whether your car has a dedicated tow bar wiring kit available can be found on the chosen tow bar product page).

Universal Wiring Kits

Universal wiring kits are needed to connect the tow bar electrics to the car electrical system. In some cases, mostly in modern cars, a bypass relay will be needed when fitting a universal kit, this is to ensure the towing electrics and vehicle electrics co-ordinate voltage/ power and wont detect the drop in voltage/ power as a fault.

Things to consider before purchasing a universal wiring kit

  • Trailer Stability Control

Some modern vehicles have trailer stability control programmed as an extension to the cars regular stability control system, however, if a universal wiring kit is fitted to your vehicle, the trailer stability control function may not activate and become null.

  • Vehicle Warranty

If your vehicle is still under warranty then you might want to consider the affect of fitting a universal wiring kit. Most warranties will specify that any tow bar wiring fitted must be equivalent to the wiring supplied by the vehicle manufacturer. Meaning, they prefer a dedicated wiring kit over a universal wiring kit.

Dedicated Wiring Kits

Dedicated wiring kits are made to fit a specific car make and model. Unlike universal kits, dedicated kits work in coordination with the vehicles existing electrical system allowing it to run as functional as it was intended to by the manufacturer.

The advantage of a dedicated wiring kit is that the vehicle will know when you are towing and will automatically adjust the following systems (only if the vehicle has them):

  • Brake electronics
  • Engine electronics
  • Cruise control or A.C.C
  • Parking aids
  • Reversing cameras
  • Lane change assisting
  • Suspension system
  • Engine cooling system
  • S.P

Things to consider before purchasing dedicated wiring kits

  • Some vehicles need a compulsory download from the main agent to make the vehicle aware that these towing electrics are fitted dependent on make or model of the vehicle.
  • More often than not, dedicated wiring kits are expensive in comparison to universal.
  • Dedicated wiring kits in the majority of cases connect directly into the manufacturers dedicated socket. In some vehicles it may be necessary to run other cables through the vehicle, this can make fitting more difficult.

Bypass relay

A diagram of a tow bar electrics bypass relay:

bypass relay

N.B. Fog light function- to activate fog lights on attached trailer, turn fog lights on then immediately off. Fog lights will now only be illuminated on the trailer. As a reminder, a warning buzzer will activate every 90 seconds in the vehicle. To cancel this function, turn off side lights.

For vehicles with combined brake and tail light you have to discard (not connect) the black and brown wire on the bypass relay ) input a side only) and connect the single wire on the vehicle to the red wire on the bypass relay.

Split charge relay

A diagram of a tow bar electrics split charge relay:

split charge relay

Split charge relays or tandem charge relays are used to divert charging current from the alternator on a towing vehicle and divert charge via the 12S socket to the leisure battery in a caravan or catering trailer. Split charge relays are intelligent relays that can automatically sense when the vehicle that is towing needs the charge for its own battery and so switches back the charge to the vehicle.

When wiring with a split charge relay only one of the 12v permanent live allocations is needed for most applications (either output can be used). Split charge relays are wired into the grey 12S socket or 13 pin socket of tow bar electrics and come in 2 sizes, 20 amp and 30 amp. We only offer 30 amp split charge relays as it is suitable for all vehicles including those with gas fridges.