Basic wiring of towbars to older cars is fairly simple, but wiring to a towbar with cars of today can be confusing. There are two types of connectors used when wiring a towbar to your vehicle: a 12N or a 12S connector. Both are similar in appearance, but the difference is the function of the pins and the purpose of the coloured wires connecting to them. Some trailers require less wires to be connected than are provided, but the colours of wire still represent the same functions.
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Connectors of the 12N type are used on towbars connected to regular pulling vehicles (cars, trucks) that power road lights (indicators, brakes) while 12S sockets are used when towbars are connected to motor homes or caravans and are used for auxiliary systems (such as a fridge or battery charger). The power needed for the trailer indicators, brakes, fog lights and sidelights are provided by the connectors which are located on both the vehicle and the trailer, and each coloured wire connects to this for a specific purpose. On most vehicles, the cover of the 12N connector is black and contains seven pins, numbered 1 through 7. Each colour of wire has an intended connection to these pins. The 12S connector is typically grey in colour and its pins are also numbered, but the colours of the wires serve different purposes in this connector.
The yellow wire connects to the pin labelled "1" and works the left-hand indicator (turn signal) with a 12N connector. On a 12S connector, yellow powers the vehicle's reverse lights.
The blue wire connects to the pin labelled "2," which in both connectors is a female plug, and operates the rear fog light with a 12N connector. In the 12S connector, the blue wire powers the battery charge.
White, connecting to the 12N and the 12S connector pin labelled "3," is your earth or ground wire for both types of connectors. It connects to the negative terminal of the battery that is connected to the metal frame of the vehicle.
The green wire connects to the pin labelled "4," and operates your right-hand indicator (turn signal) with the 12N connector. In the 12S connector, this wire acts as a power feed.
The brown wire of your towbar connects to the pin labelled "5," which is a female plug. In the 12N connector, it operates the right-hand side lights. On the 12S connector, the brown wire is intended for sensing devices and taillights.
Red wires indicate your stop or brake lights with a 12N connector. The red wire is connected to pin "6" on both connectors. In the 12S connector, the red wire powers the fridge. Caravan Products recommends when wiring a motor home, the red wire is connected through a split relay when connecting towbars to vehicles made in 1999 or later. Older model vehicles are wired differently and you should consult a professional for these. A split relay allows a secondary battery (such as a motor home battery) to be charged by the vehicle's system, but it isn't used in engine starting. It also prevents the starting (primary) battery from being drained by the other equipment when the engine is off.
The black wire on your towbar is connected to pin "7." In a 12N connector, it operates the left-hand side lights of your vehicle. In a 12S connector, the black wire and pin "7" function as the ground for pin "6" (your battery connector).
Less Than 6-Wire Connections
Some older connection styles are still in use; for example, 4-way wire connectors utilise only the yellow, green, white and brown wires, operating the left indicator (yellow), right indicator (green), ground (white) and number plate and taillights (brown) as they would in a 7-way connector. There are also 5-wire systems, which add a blue wire to operate braking systems and auxiliary power.
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