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Trailer Wiring

Wire Colour
Left Indicator
Fog light
Right Indicator
Right Side Light
Brake Lights
Left Side light

Front of plug view

Trailers must be equipped with running lights, brake lights and indicators. They do not need to have fog lights or reversing lights. So that these lights work in sync with the cars lights the trailer must be hooked up to the internal wiring loom of the car. this sounds hard but is not that difficult.

Instructions can be found usually in the car oners handbook. You can use T-connectors to tap into the cars existing wiring quite literally following the wire that comes from each bulb. The wire to each bulb is a positive supply and the bodywork of the car is negative or earth.

• Attach a yellow wire to the wire that goes to your left indicator bulb and run that wire to pin 1 on your connector

• Attach a blue wire to the wire that goes to one of your fog lights and attach this wire to pin 2

• Attach a white wire to the bodywork of your car (Usually to the casing that holds your rear lights array) and run this wire to pin 3

• Attach a green wire to the wire that goes to your right indicator bulb and run this wire to pin 4

• Attach a brown wire to the wire that goes to your side lights. Note the diagram says right side light but they have a common supply so it is not that important which one you use. However side lights are sometimes brake lights aswell. Inside the bulb there are two filaments one which lights up for side lights and a brighter burning filament which lights up for brakes. The bulb will obviously have two wires going to it.A test meter will help you determine which is which as if you piut your side lights on your car on and don't press the brakes, the wire that has 12v running through it will be your side lights. Connect the brown wire to this a run it to pin 5. the other wire that goes to this bulb will be the brake lights and you can attach a red wire to this wire and run it to pin 6

• Attach a black wire to your other side light (left as in diagram) and run this wire to pin 7. Having two side light connections is only necessary if you use parking lights where you can leave your indicator on when parked with the ignition off and only that side light remains on.

If you do not wish to use this function then you could connect pins 7 and 5 together and only tap into one side light.

The are lots of type of connector available but you should choose one which can handle all the wiring in one plug as in the diagram. Mount the connector to the car neatly and make sure no wires are hanging down where they could become detached. Wire up the plug on your trailer in the reverse of the diagram so that the right pins connect to the right circuits.

Note: Not all trailer wirings are the same and some trailers do incorperate fog lights and reversing lights. Caravans can also take a contant 12v supply. These will have to be taken into consideration and will need connection plugs and sockets with more pins.

Some manufacturers provide a wiring harness for a towing connection details of these can be found below.

Wire Color By Manufacturer
Dual Purpose Bulb System
Wire Function Wire Color


Ford Chrysler Jeep Toyota Honda Mazda




Orange W/ Blue Stripe Brown Brown Green W/ Yellow Stripe Green W/ Yellow Stripe Green W/ Yellow Stripe
LEFT TURN & BRAKE LIGHTS Yellow  YellowLt Green Orange Stripe Dk Green Grey W/ Black Stripe Green W/ Black Stripe Green W/ Blue Stripe Black Stripe
TAIL LIGHTS Brown  BrownBrown Black W/ Yellow Stripe or Black Blue Red W/ Green Red W/ Black Stripe Green or Black Stripe
GROUND White Black Black or Grey Black Black & Black Black or White Black Black
Single Purpose Bulb System
BRAKE LIGHTS Use Converter Pink or Lt Blue Red W/ Green Stripe White Blue W/ Black Stripe Green W/ Red or White Stripe Green W/ White Stripe Green or Green W/ Red Stripe
BACKUP LIGHTS Red Lt Green Black W/ Pink Violet Brown- - -
ELECTRIC TRAILER BRAKES Connect To Blue Wire From Brake Controller