On the list of things no one should have to bring their vehicle into a mechanic to do, wiring up off road lights is up there. Especially with all this lockdown stuff going on, many of us are finding ourselves with more time on our hands than we really know what to do with.
A wise man once said:
“Everything looks better with big driving lamps bolted to the front end.”
That wise man’s name? Abraham Lincoln. Just kidding, it was me. I am the wise man. Why are you laughing? Anyway, it’s true! Everything from a Toyota Corolla, Jeep Wrangler, SVT Raptor, or even an old Volvo wagon just looks better with a sweet set of off road or rally lights. Fact.
How to Wire Auxiliary Lights:
So there are a few ways you can go about wiring these up, and two main schools of thought when it comes to how to turn them on:
- The lights come on with the brights
- The lights come on with a separate switch
A lot of people prefer to have them come on with the headlights, and that makes for a clean interior install, as you don’t have a non-factory switch standing out on your dashboard. However, once you start adding more lights and accessories like selectable lockers or a winch, adding switches becomes inevitable. I’ll go over each method here in as much detail as I can while keeping this guide general enough to work for the Wrangler owner AND that weird Volvo guy.
What You’ll Need:
The lights or light bar you bought probably came with a wiring kit, but not all do. In that case, you can either buy a wiring kit, or put yours together with this basic list (might need to add or subtract things for your application):
Wiring: Depending on how much power your lights will be drawing, you’ll need anywhere between 14 and 10 gauge wire. When in doubt, just go up a size and you won’t regret it (smaller number gauge means bigger diameter). It’s not a bad idea to get 20 feet plus, as you’ll most likely end up using more than you thought, and it’s always good to have around. Smaller wiring can be used for grounds and between the switch and relay, and it’s a good idea to stay consistent on colors, so black/brown for ground/earth and red for power.
Relay: Some people try to just wire from the light to the switch and to the battery — but this isn’t a great idea. Most lights will more power than your average in-cab switch can handle, whereas a the right relay can handle the voltage safely, and handle bigger power requirements down the line. Look for a 12v DC 30/40 amp automotive relay.
Switch: Optional if you’re not wiring the lights to come on with your brights — however some people choose to do both, in case you want to just use your brights without the lights coming on. This is handy in places like California where we’re required by law to run covers on auxiliary lighting on the street.
Fuses: One 30 amp fuse should be sufficient for most applications to be wired between the hot side of the battery to the relay. You’ll also want a small fuse for your switch in the cabin, a 10 amp fuse should be plenty for that. With fuses, it’s always a case of better save than sorry, as this is how fires happen.
Various connectors: Spade connectors are used often in these applications, as are ring terminals for grounds. With all the varied weather and moisture even street cars see, it’s a good idea to use well insulated connectors, heat shrink wrapping, and to tin exposed copper before it goes into any connector.
Zip ties: If it can’t be fixed with zip ties and duct tape, then it can’t be fixed. Nah, not really, but these are essential for keeping wiring tucked away where you need it, looking clean and keeping your wiring safe.
Wiring step by step:
1) Mock up where you want everything to go:
It’s always a good idea to do this before you go drilling holes for switches, relays, or lights. Measure twice, then measure two more times, and then cut. This way you can get a lay of the land for where wiring will have to be run, and you can mess around with where you want the switch to go. This will give you a good idea on how long the wiring needs to be and where the grommets are on the firewall to poke through. It’s also not a bad idea to bench test everything first before wiring to make sure everything works.
In this setup, we will effectively have two wiring circuits:
- High-amperage circuit: Battery > fuse > relay > lights > ground
- Low-amperage circuit: a fused power source > switch > relay > ground
These two circuits demonstrate the job of the relay in this scenario. Your switch receives 12v power from the factory ignition or accessory lines (more on that later) just to send the signal to the relay to open or close. The relay does the heavy lifting here with an audible click, connecting the high-amperage circuit between the lights and the battery.
You want to keep your wiring out of the way of any moving assembly and away from high heat sources, such as your exhaust. Look at where the manufacturer ran wiring from the factory and follow that where possible. They’re smarter than you.
2) Disconnect the ground terminal on your battery:
Anytime you’re doing anything involving electrical, just do us all (and your heart) a favor and just disconnect the battery, and make sure the terminal doesn’t ground out on anything. At the very least, your mother will thank me.
3) Run the wiring through the firewall behind the dash:
There should be some rubber grommets on the firewall where your factory wiring loom goes through (if yours doesn’t, it’s not a bad idea to add one or protect the wires against the exposed metal in some way).
Now is the time to apply any heat shrink or wire loom tubing to your wiring to protect against heat, moisture, and exposed metal.
4) Wire and mount your switch, or tie into existing wiring if utilizing a factory switch:
If you’re tying into your brights or fog lights switch, now is the time to tap into those wires. Again, nothing is worse than tracking down intermittent issues caused by shoddy wiring, so use good, insulated spade connectors, tin your wire ends, or solder the connections. Twisting some copper together and smothering it in electrical tape isn’t the answer.
Wire and mount your switch somewhere accessible from the driver’s seat. For power, you’ll most likely want to tie into a 12v line that comes on with the ignition or accessory positions (you’ll need to research your factory wiring to find these). On ignition, your switch will receive power only when the vehicle is running, on accessory the switch will receive power with the key in and turned to the first or second click.
You should be able to find a ground wire to tie into, but I suggest wiring a ground yourself to the firewall under the dash. There will probably be a ground mounted to the firewall, but you can tie into an existing bolt if not, or drill your own. The important part is to have exposed metal contact for a good ground.
5) Mount and wire the relay and main fuse:
Many people like the cleanliness of mounting it on the firewall where other wiring sits, though some people choose to mount the relay closer to the battery, which isn’t a bad idea. Your main fuse should be about as close to the battery as possible. This is your safety net in case anything goes wrong, such as a wire shorting out on a sharp bit of metal trim. Better a fuse blowing than having wires melting and starting a fire.
Connect your switch wiring to the relay (the diagram above should apply to most common 4-post relays, your mileage may vary). Then run your hot wiring out to the lights, again, wire loom tubing, insulated spade connectors, heat shrink, and tinned copper are your friends!
6) Mount, wire, and ground your lights:
If you’re drilling holes to mount your lights, make sure to measure more times than you feel is needed before drilling. From there, use a small bit to drill a pilot hole, and then step up from there. You don’t want to get everything done and then have your buddy point out that one of your lights is mounted a little off from the other.
Some lights are self grounding, meaning they ground themselves through the hardware to whatever you’re mounting them to, but I recommend running your own ground, as your bumper or roof rack might not provide the best ground. You can tie into a factory ground under the hood, or go back to the negative terminal on your battery.
7) Tie up loose ends and aim your lights:
Zip tie your wiring up out of the way, double check your connections, and for god sakes, clip your zip tie ends, you filthy animal. Once you’re sure everything is set correctly, go ahead and reconnect the negative terminal on your battery and test your lights out!
Park your rig about 20-25 feet away from a wall and aim your lights how you need. Are you going for close up fog lighting, or long distance visibility? Now’s the time to get them sorted.
8) Don’t be that guy:
OK, so you’re now part of an elite club of people who threw some big off road lights on the front of their car. Congratulations and welcome! Now it is my obligation as a longtime member of this club to tell you to use this great power responsibly.
Treat your auxiliary lighting like your brights. Don’t run them on the street while anyone else is around that you might be blinding, or don’t use them on the street at all depending on your state laws. The people running their bright-as-the-sun light bars on the street give us all a bad name, so don’t be that guy. No one is impressed by your ability to remove other driver’s functional vision. Don’t do it.
Have any questions or comments on this guide? Anything I left out? Have any ideas for what DIY projects we should cover next? Drop a comment below or shoot me an email at firstname.lastname@example.org!