Towbar 12N Wiring - General guide

Before you start

Examine the car carefully to see that all electrical circuits are working correctly and that no warning lights are showing.

Take into account:

With many modern cars it is best to take power from a source such as the bus bars at the back of the fusebox. If the car has a battery status display, it is probably monitoring power input and output, and using the alternator only to replace the power it sees being consumed. If you take power directly from the battery in such cars, the system will not replace it and the battery will run down.

Decide whether to disconnect the battery. Consider the following.

  • Would disconnection disrupt memory circuits, etc? (You may need a device to preserve memory circuits )
  • Can you make your electrical connections safely with the battery connected?

General Instruction, 12N boot fitting relays and monitors

  • Find a suitable cable entry point, close to the trailer socket. (If you have to drill, select your spot with care, treat the edges of the hole with anti-rust paint, and insert a suitable grommet to protect the cable.)
  • Wire the trailer socket, as shown in Chart A and mount it on the towbar. If you are using a 13-pin socket, the pin numbers for the "N" wiring are the same as for 12N 7-pin sockets.
  • Lead the trailer socket cable into the boot through the prepared entry point. Make sure the cable is a snug fit in any grommet it passes through, to prevent fumes coming into the car.

If you need to take a power source for a bypass relay, etc.

  • Route your power source cable(s) to the power source. Fit appropriate fuses in line in the cable, close to the power source. Do not connect yet .
  • When routing the cable, take care to route it where it will not be cut or crushed. Pay particular attention to points where the cable passes through bulkheads, etc.

Connection: In all cases

  • Use an LED type probe tester to identify the appropriate wires in the vehicle loom. Use an LED type, tather than a standard filament bulb because LED type take only tiny currents when you probe.
  • Follow the instructions in Chart A below and connect together your trailer socket cable, your relay(s) and/or monitor and the appropriate wires in the vehicle loom.
  • If applicable, connect your power cable to the power source and insert the fuse(s).
  • Use a suitable test board to test the circuits, preferably with the car alternator charging. Make sure any "Tell-tale" warning light or buzzer is working correctly, monitoring the trailer flashers.

Chart A

Pin No.
to? Relay wire
colour or
terminal No.
Relay wire
colour or
terminal No.
to? Vehicle Circuit
1 Yellow to See relay details to LH Flasher
2 Blue to See relay details to Fog Lamp
3 White to Chassis White to Chassis earth
4 Green to See relay details to RH Flasher
5 Brown to See relay details to RH tail light
6 Red to See relay details to Brake Lights
7 Black to See relay details to LH tail light