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Defender Headlight Wiring Upgrade

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Hi All

I've been meaning to sort the headlight wiring on my Defender for quite a while now and I finally got round to it last weekend.
I didn't really like the idea of the off the shelf wiring kits like the Boomslang one etc. as I wanted everything to be as original as possible so didn't like the idea of running an extra power supply to the battery, as there is nothing wrong with the original supply. In the end I decided to do it as described below.

If you decide to follow the steps below you do so at your own risk blah blah blah and if you set something on fire or your wife leaves you don't blame me.

I was doing this on a 2003 Defender 90 TD5 but you could adapt it for your model.

I used 1 mm2 thin wall cable for the low current connections to the relay coils and 3 mm2 thin wall cable for the high current side.



I've used three relays as the original setup uses a separate power supply for main beam flash, and this setup is as close as possible to keeping the same functionality as original.
For the dip beam I have connected into the dim dip relay as I had this bypassed anyway.



Once you have made up your relay holders following the diagram above, the first thing to do is to remove the cowl under the steering column, the instrument cluster and the drivers side speaker. You will see three relays behind the instruments, unclip the dim dip relay holder (I decided to remove the holder to make room for the new relays) and move the right hand relay to the left, you should now have room to screw in the three new relays on the right hand side.


Now if you unclip the two original relays you should have enough slack on the cabling to pull the dim dip relay holder out through the speaker hole to make access easier. now you need to figure out which of the two Blue / Red wires goes to the switch and which one goes to the lights, so grab a multi meter / test light and switch the lights on and see which one has 12 volts on it, this is the switch side.

Connect the switch side and headlight side Blue / Red wires to the relays as per the diagram, I decided to remove the pins from the holder and cut and solder the connections, but you could just push some male pins into the holder if you like. At this point I also used the earth connection in the dim dip relay holder to earth my relays.

Put the two original relays back on their mounting tabs and find a secure place for the dim dip relay holder up behind the dash.


Next unplug the headlight switch and the column switch (the one that does dim and main beam) and with a bit of fiddling you should be able to pull them across to the right hand side and through the speaker hole. once you've done this you need to splice into the brown / blue that goes to the headlight switch and the brown / purple that goes to the column switch. You now need to cut the blue / white that goes to the column switch and connect it up as per the diagram.


Now tape everything up neatly, connect the headlight and column switch back up and switch the lights on to give it a test.





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I did measure the voltage at various points but this was a long time ago (it's taken me a while to get round to actually doing the job) so I can't remember the figures. The main area of concern was the switch, the column switch if I remember correctly, as the voltage drop across the switch when under load was significant. I don't doubt that you could achieve a marginally higher voltage at the lights by running a dedicated supply from the battery and putting the relays under the bonnet, as you would end up with a shorter cable run and fewer connections, however one of the criteria for me was to keep everything as original as possible. The improvement in the light output is like night and day so I'm happy with the small compromise.

I've taken the supply from the input to the headlight switch which Is fed from the under seat fuse box.


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  • 4 years later...

Hello, I’m looking for a 2003 TD5 Defender wire loom. I had a break in and someone cut the wires which connect to the flasher, headlight dipper and wiper motor relays .  I need to replace the wiring loom  (hopefully with the same wiring coloring so to allow for easy re-connection. I also need the relay holder as well , (I have the 3 relays) Does anyone know here I can purchase this??? 

I'm based in Kyoto Japan

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