Installing LED Trailer Lights with Separate Components

1 x TS1465 25 Watt 240V Soldering Iron

1 x TH1827 Heavy Duty Wire Stripper / Cutter / Crimper with Wire Guide

1 x TH1632 Gas Blow Torch with Butane gas (for heatshrink)

1 x TD2022 7 Piece Screwdriver Set

1 x TD2192 5 Piece Combination Spanner Set

1 x TD2800 20V Cordless Drill Set

1 x TH1812 5 Piece Stainless Steel Tool Set 4 Pliers and 1 Cutter

1 x TH1984 Heavy Duty Pliers

Start by removing the old lights. We cannot be too specific about this because of the variety of designs, but in general, there will be two or more bolts in each light cluster with nuts on the other side of a plate of metal. Some designs do use self-tapping screws from the front, and some poorly-placed lights may be attached to areas where there is no access for nuts and bolts, like hollow section steel instead of plate.

Cut the wires close to the light cluster, and at the plug near the drawbar. Pull out any wiring that you can, then get under the trailer and look for any more.

Having removed the old lights during preparation, hold the new lights up to the mounting points to see if screw holes align. These lights have a plug in the back while the old lights did not, so we need to enlarge what was the wiring hole to take the plug. For this, we used a step drill. We also needed two new mounting holes. We later sprayed everything with a coat of cold galvanising spray to keep rust away.

NOTE: We mounted our lights with the number plate light facing downward, because we are not using it. If you are using the number plate light, the bolts will be vertical, not horizontal like ours are.

Next, mount the new lights. Do up the nuts over the bolts moulded into the light fittings. You may wish to add some thread fixing compound to give extra insurance against loosening. Repeat this process for both sides, and if you are fitting a number plate light, for that too.

Tape the new wire onto the end of the rope on the outside of the drawbar end. Carefully pull the new wire through from the underside of the trailer, leaving enough out for the vehicle connection.

This pic shows the new wire coming out of the trailer’s drawbar.

Here, you see the new wire going underneath the drawbar.

This trailer has nowhere else for wiring to be run enclosed, but it does have some holes in the chassis components for wiring. Before adding the wire, we added some rubber grommets to help prevent the wire from being cut through by repeated rubbing on the metal due to movement.

NOTE: If you are adding a separate number plate light, you can add it to either the right or left light cluster wiring, depending on where your mounting is. The black wire of the LED light goes to the white ground wire on the loom, while the red wire of the LED goes to the brown tail light wire on the loom.

With the five core wiring loom having been drawn all the way to the back of the trailer, make the connections to the lights. Cut the loom near one side of the trailer, depending on where your trailer's best cable path is, and strip the cores. You need four of the five wires, which is why we suggest you cut the lot instead of trying to strip some of the outer jacket without cutting the cables: It's not worth the effort to keep a single core*.

On this side, we need tail lights, brake lights, right-hand indicator, and ground. That's brown, red, green, and white in that order. Strip the cores, twist the strands, and tin them with solder if relevant. Add glue-lined heatshrink to each of the colours on the single core side, then solder or crimp the wires colour for colour to the tail from the light cluster and the core from the loom that will continue to the left-hand side. The yellow wire for the left-hand indicator just needs to be soldered or crimped together, as no wire needs to be added. The other colours now have three wires.

Slide the heatshrink up and heat it thoroughly.

Run the loom from the light cluster you have just wired, under the chassis behind the tailgate. This trailer has space for it there and several metal loops for cable holding. Your trailer may have a different ideal spot for the wiring. Once the loom reaches the left-hand cluster, you can cut the excess length and repeat the above process, but the wires needed now are: Tail lights, brake lights, left-hand indicator, and ground. The process is the same, but in this example, we have added our number plate light here. The other major difference is that there are only two wires in most cases, not three, because this is the end of the line. The groups of three wires in the photo are the added number plate light.

The final primary task is connecting the plug. The seven pin flat plug has screw terminals at the back, under a cover which is retained by lugs at the front and a nut as the back, The top and bottom of the connector each have half of the threat for the nut. Unscrew it, and separate the halves.

Strip around 6cm of the outer jacket to expose all of the cores, then strip 5mm of each one. Twist the strands into a firm bundle, insert into the appropriate contact, and screw down onto it firmly. Ensure you have metal to metal contact and that the screw has not contacted plastic insulation instead.

Wire according to the diagram earlier. When looking at the top of the plug, the wire order should be, from left: Green; brown; empty; white; empty; red; yellow. The two empty spots would be used for reversing lights and electric brakes if relevant.

With the wiring done and checked, screw down the cable strain relief retainer if there is one. Close the cover by sliding the lugs into the front of the housing and doing up the nut at the back.

To finish off the wiring, we went back under the trailer and added split-loom tubing and some self-adhesive cable tie mounts. Split-loom tubing covers the wire and adds extra abrasion and impact damage resistance. It is a ribbed tube similar to vacuum cleaner or pool cleaner hose, but smaller, with a slit running its length. It can be cut with a knife, then pressed over the wire to help protect it.

The adhesive cable tie mounts help add security, because there are not always enough tie points on the chassis to keep the wire really secure or stop it sagging to where it can catch on something.

Other finishings may be to add silicone sealant or some sort of caulking compound to the joins where two or three cables go into the same end of a piece of heatshrink. While glue-lined heatshrink should flood the join with glue, it is not always enough and extra sealant helps keep water out.

Some trailers have hollow sections or channels where wiring can be located. Others have the ends sealed or are built in ways that do not allow wiring to be enclosed, and so an external attachment is needed. Whether you are installing with a kit or components, you might need to view both of the following instructions. For our install with individual parts, we ran some wiring inside structural sections of our trailer where we could. For our kit, we ran the wire outside the structure all the way, because the plugs are already installed on the kit and there is a Y-connection in the middle. Therefore, we show the relevant attachment methods in those instructions, but you may be mixing and matching.