Over 60 Years Experience with Towing Brackets and Trailers

Wiring Guides


An important but often overlooked aspect of towbar fitting is the wiring required to power trailer lights and caravan internal electrics.

Watling Engineering, WiringThe basic wiring to the plugs and sockets is fairly straightforward, however the fun starts when you are required to fit audible buzzers, relays and bypass units to cope with the increasingly complicated cars of today.

We are fully conversant with all aspects of towbar wiring and are stockists of Ryder electrical equipment who are market leaders in the field of towing and trailer electrics and have a reputation for quality and durability.

Towbar Wiring Guides

Listed below are some basic 12N and 12S type wiring diagrams that will help in vehicle wiring for both road lights and caravan internal electrics.

Alternatively, we are willing and able to look at any wiring problem here at our workshops.


WIRING DIAGRAM FOR 12N TYPE 7-PIN Black socket or plug for vehicle road lights

Colour Terminal Purpose Looking at the Socket towards the plug. Looking at the Plug towards the socket.
Yellow 1 (L) LH Indicator Watling WD Black Socket
Blue 2 (54G) Rear Fog Light (or Aux.)
White 3 (31) Earth
Green 4 (R) RH Indicator
Brown 5 (58R) RH side Light
Red 6 (54) Stop Lights
Black 7 (58L) LH Side Light


WIRING DIAGRAM FOR 12S TYPE 7-PIN Grey socket & plug for caravan & trailer interior power.

Colour Terminal Purpose Looking at the Socket towards the plug. Looking at the Plug towards the socket.
Yellow 1 (L) Reverse Light Watling WD Grey Socket


Battery Charging or Power
White 3   Earth
Green 4   Power or Battery Charging
Brown 5   Warning Light for pin 1
Red 6   12V Refrigerator
Black 7   Spare



Because the Swift Hitch is completely wireless, it can be used on both the front of your vehicle for hitching up your Watling Front Towbar as well as for your rear towbar. Click here or on the photos for more information



WIRING DIAGRAM FOR 12N TYPE 7-PIN INCLUDING REAR MOUNTED AUDIBLE BUZZER for most cars that do not require bulb failure bypass relays

Watling Diagram for 12N Type 7-Pin Including Rear Mounted Audible Buzzer


Watling Diagram for Self Switching Relay on 12S Socket


Watling Wiring Diagram for Double Relay on 12S Socket


FIRST: Check and test the fuses on all circuits

SECOND: Ensure that there is a good clean EARTH connection to the vehicle body, the 7-pin socket, the trailer 7-pin plug and the trailer lamp units.

If one circuit does not function check and test the fuses, check and test the bulbs. If fuses continue to blow, calculate that the fuse is the correct size for the load on the circuit (Watts/Volts = Amps eg 4x21w / 12v = 7A). The fuse rating should be approximately twice the load to allow for surges.

Look for a “short circuit” – bare wires or contacts touching Earth along the loom, the socket, the plug or in the lamp units.

If any bulbs flash or dim out of sequence, check ALL the earth connections.

Other checks you can do include:

  1. Clean off all paint, dirt or rust from around the earth point, fix a ring tag to the white wire from the 7-core and fix securely to the earth point, smear with petroleum jelly.
  2. Clean the bulb contacts and holder.
  3. Test the other six wires for continuity across the connectors and to the lights.
  4. Test the screw connections in the socket, if there is any sign of corrosion replace the socket. Discard any socket covers or rear seals as these only promote corrosion through condensation, ensure drainage from the socket. Ensure that the 7-core is lead through grommets in metal surfaces and prevent chaffing at any point. Clip the 7-core back to one of the socket screws with a P-clip.
  5. Check and clean the individual pins in the socket, spreading the male pins slightly.