I’ve been driving the X daily since 2006 so I’ve been putting up with the headlights for a loooong time. I’ve tried every halogen option you can buy and aside from the slight color variations none of them were very good, the headlights just always seemed dim and underpowered.
I got to thinking about it recently again after another winter of not being able to see the road and decided to finally do something about it. After researching it more I found some sites selling custom harnesses for the headlights that promised to make even stock wattage bulbs perform brighter because they use relays to pull power directly from the battery and send it to the bulb with much thicker wire than the factory setup. After looking at it I realized I could easily build my own upgraded harness and also use higher wattage bulbs.
I wanted to find out exactly how much power would be used by the new lights and what wire gauge would support them with minimal voltage drop. Basically too thin of a wire doesn’t allow all the power to go through and when the power can’t get through it creates heat. This can lead to fires which obviously we all want to avoid but it also leads to dimmer headlights.
After a bit of math I was able to come up with a decent plan, I would run a single main power line off the battery ( about 6 inches of 2-gauge copper strand wire) to a splitter that had 2 short 10-gauge wires each connected to an in-line fuse. By having two power sources fused separately the low beam and high beams would be on different circuits so if one went out the other would stay active and then you don’t end up without headlights in the case on of them goes out. Also this allows for a smaller amp fuse to be used on the low beam circuit and a higher amp fuse on the high beam circuit.
Here’s some info on the factory bulbs vs the 85/100 watt bulbs:
|9007 55/65 watt (factory spec)|
|Low Beam: 4.58 amps per bulb|
|High Beam:7.08 amps per bulb|
|Hella Optilux 9007 85/100 watt|
|Low Beam: 5.42 amps per bulb|
|High Beam: 8.33 amps per bulb|
After calculating the amp load I found an online voltage drop calculator, put my numbers in and found that 12 gauge wire at around 5 feet would only have a voltage drop of a little less than a percent. Perfect. With everything planned out I got online and started ordering. Here’s the full parts list:
1. 12 gauge wire, Noble brand
x1 (15 feet pack)
2. Hella Optilux 85/100 watt bulbs
x1 pack (2 bulbs)
3. Pico 40 Amp Waterproof Relay
4. 9007 Male Socket with 12 Gauge Pigtails
5. 9007 Female Sockets with 12 Gauge Pigtails
6. 12 Gauge butt splices
Various shrink wrap tubes for wires.
Braided wire sleeve, ¼” type
In-line fuse holder
Copper 2-gauge Compression Connector
Rubber Splicing Tape
With all the parts you have everything you need to assemble the harness. As a sidenote I used a 2-gauge wire I had already in my scrap wire collection combined with a 2 to 10-gauge splitter that I connected the fuses to. If you don’t have anything like that you can get away with just using x2 12-gauge wires from the battery.