Trailer light, wire colour coding and LED Upgrade

There are 7 wires that come from the trailer socket and go to the trailer light units in the UK, they are coloured as follows:

Not all these are used on trailer light units, some go to the left hand lights some go to the right and some are common. The wiring splits at the lighting board and not all the colours are used to operate each side and the basic board has the following colours:

• Blue Reverse lights.
• Green Right turn / brakes.
• Yellow Left turn / brakes.
• Brown Taillights.
• White Ground

Red = stop light and brake light

Black or brown (usually black) = Trailer tail lights and Number plate lights, it shines through a transparent window.

Green = right indicator/turn

Yellow = left indicator/turn

White = neutral/ground

The images above show a general layout left hand side has 4 coloured wires yellow, (left indicator) red, black and white (earth).

The right hand side has green, (right indicator), red, brown, white (earth). If you have issues with trailer suspension units sagging the take a look at this related post.

So now having established how the wires and their colour coding appear at the left and right trailer light units some will have noted that the build are the ‘old fashioned’ incandescent bulbs which, on a trailer have a tendency to need replacing.

The recent approach is to upgrade to LED units like the one shown below.

This is where a little care is needed because you may notice that the wires are coded for each unit. There is no left and right and the colours DO NOT CORRESPOND.

the LED colour coding is as follows:

Red = stop light and brake light

White =  Number plate lights, it shines through a transparent window.

Green = Tail lights

Yellow = Indicator/turn

Grey = earth

So in order for the lights to work correctly depending on which side you are upgrading the wires need to be joined to correspond.