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How to Wire a Car Tow Bar

Updated April 17, 2017

Wiring a tow bar to older cars is more often than not a simple task, requiring a female-end harness to be attached to a male-end harness on the trailer. Unfortunately, with newer vehicles there is a little more to it. There are two kinds of wiring kits, featuring a 12N or a 12S connector. They are almost identical but 12N connectors are used for towing trailers and most vehicles, whereas 12S connectors are used for motor homes and caravans, taking the auxiliary systems into account. Both operate 7-pin sockets with different colour-coded wires for each.

Connect the yellow wire to pin number 1. For 12N systems, this operates the left blinker (indicator). For 12S systems, this operates the reversing lights.

Connect the blue wire to pin number 2. For 12N systems, this operates the fog lights. For 12S systems, this powers the battery.

Connect the white wire to pin number 3. For both systems, the white wire is the earth.

Connect the green wire to pin number 4. For 12N systems, this operates the right blinker (indicator). For 12S systems, this is the power feed.

Connect the brown wire to pin number 5. For 12N systems, this operates the right sidelights. For 12S systems, this operates any sensor systems and the rear lights.

Connect the red wire to pin number 6. For 12N systems, this operates the right break-lights. For 12S systems, this powers the fridge in the motor home or caravan.

Connect the black wire to pin number 7. For 12N systems, this operates the left sidelights. For 12S systems, this acts as an earth for pin 6.

Warning

Make sure your wiring is functioning correctly. It is illegal to tow a vehicle or trailer without the electrics functioning.

Things You'll Need

  • Tow bar wiring kit
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About the Author

Joe Faulkner-Edwards has been a freelancer for the BBC since 2008. He writes and researches innovative new factual entertainment formats and output-related material for BBC Online. Faulkner-Edwards is also a health and fitness expert. His health and lifestyle articles have been featured in "The Leeds Student" newspaper. He holds a Bachelor of Arts in broadcasting from the University of Leeds.