12N Single Electric Towbar Wiring Information

Single 12N towbar wiring kits are most commonly used on older vehicles which do not have any on board computers or safety devices, one example is vehicles with a bulb failure device on the dashboard, these type of vehicles will require a bypass based relay or a plug in wiring kit.

How do i get the cable inside the car?

Most vehicles will have a hole that is filled with a solid grommet somewhere on the underneath of the vehicle at either side, then simple pop out the existing grommet and replace with the one provided in our kits, this will prevent damage to the cable, then simply and possibly with the aid of a little lubrication push the wire up through the grommet to the point where connection will be made.

How do i know which cables to connect to?

The only sure way of finding which colour wires perform which operation, is to use a wiring tester. These devices work by having a bulb inside the tester, so when for example you need to find which wire is for the side light, simply switch on the side lights and test each wire with the tester, when the correct wire is found the bulb will light up to indicate this, then all you have to do is connect the wire on the 7 core cable to the appropriate wire and the connection will be made.

What sort of connections should I use when connecting the wires?

There are two types of connections that can be used whilst connecting cables together, you can use displacement connectors more commonly know as scotch locks or you can solder the joints together.

Scotch Locks

These are the easiest and quickest of ways to connect the wires together, these have been approved by the NTTA as a secure way of fitting your towbar electric cables together despite what certain towbar fitting centres may say when you want to book in to have your towbar fitted thus increasing the overall price of the job. The only problem that can occur from scotch locks is that a cable may become loose from the connection and that operation will fail.


Soldering cables together is a much more time consuming way of installing your towbar electrics, although it can give a secure connection with a less likely chance of the wires becoming loose, if the connection board is not properly protected and water gets into the area where the connection board is stored it can corrode and lead to everything failing and the whole thing being replaced.

How will i know that everything works?

Testing at the end of the installation can be done either by using the tester and placing the tester into the socket on the outside of the vehicle at the appropriate point at which you are testing (see diagram on right) for example if you want to test the brake lights, have someone or something heavy placed on the brake pedal and insert the tester into appropiate position on the socket, in this case position 6, if the connection is right the tester will light up until the pressure is taken off the brake and the bulb will then go out.

There is a towbar testing device available which simple plugs into the socket and lights up every time an operation is performed successfully.

The third way of testing is simply by connecting up your caravan or trailer and checking the lights as the operations are being performed, if an operation does not perform and you have checked the connection of the wires, check the bulbs on the trailer/caravan to see if that is the problem.

What if i don't use a bypass relay or plug in kit?

Not using a bypass relays or dedicated plug in wiring kit can lead to electrical failure in your vehicles lighting system. This is especially the case with newer vehicles that are fitted with complicated wiring systems. To overcome these potential failiures we strongly recommend that you check whether your vehicle requires a bypass relay or plug-in kit. You can call us on the number above or our email address.

12N Single Electric Towbar Wiring Instructions

Below is a typical example of the posistions of the wires inside a 12N plug.

How to Towbar Wiring 12n/12s Fitting Guides

Towbar Wiring Assembly

Before you start, check the contents of the wiring kit to make sure you have all the necessary components to complete the job, there's nothing worse then fitting the towbar and discovering you cant fit the electrics at the end.

The following is what is included in our towbar wiring kits.

12N prewired socket on plate
Audible buzzer relay
Scotch lock connectors
Cable ties
Wiring instructions

12N Single Electric Wiring Instructions
1. Check all vehicle lights are working correctly, switch off all lights and ignition feeds, you can do this by removing the circuit fuse to feel more secure, but take care whilst removing fuses the engine management, alarm or audio equipment may be affected.

2. Fit the 12n towbar prewired socket between the towball and towbar using the existing mounting holes and feed the cable into the vehicles using an appropriate access hole. This can be done by drill a small hole close to where you will wire the electrics and fill with the grommet provided to prevent damage.

3.Locate the wiring in the rear behind the panels (usually on one side) and select a suitable point at which to make the connections into the wires and space to mount the audible buzzer relay.

4. Strip back approx 150mm on the black 7 core cable taking care not to damage any wires inside, identify the functions for each wire by tracing the back from the light cluster using a wiring tester.

5. Connect the buzzer relay with the 7 core cable using the scotch locks provided as follows:

6. 12N Socket          7 Core Cable                   Connection
      Pin 1                     Yellow              Yellow on the audible buzzer
      Pin 2                      Blue               Rear fog light in vehicle wiring
      Pin 3                     White                 Suitable for good earth 
      Pin 4                     Green               Green on the audible buzzer
      Pin 5                     Brown              R/H tail light in vehicle wiring
      Pin 6                      Red                 Brake light in vehicle wiring
      Pin 7                      Black                        L/H tail light in

7. Buzzer Relay Instructions
Connect together the following wires with the scotch locks supplied. DO NOT cut the wires from the vehicle rear lights.

Audible Buzzer Towbar Relay Wiring Diagram

8. Check all wires are correct and secure then replace any fuses you may have removed. plug in a 12N type trailer socket and test all lights are functioning correctly. Tape buzzer relay to wiring being careful not to cover over the sound holes on the buzzer, and place it suitable place behind dash in boot.

View our range of 12N Towbar Wiring Kits

Free Support

If you have any quiries about towbar wiring please feel free to contact us by email. Our response time is usually within 24hrs. We are happy to answer any questions you may have - info@just-tow.co.uk