Spotlights are a popular addition to any off-road vehicle, and there is an increasing number of options available on the market. Be it traditional halogen lights or an LED light bar, wiring them correctly and safely will ensure they can be used reliably for years to come.
Important: - There are various local rules and regulations around fog lights & additional headlights. Consult your local guidelines to ensure your modifications are lawful. - This article is for informational purposes only. Consult an expert before carrying out any electrical or mechanical work on your vehicle.
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Tools and Accessories
- Wire cutters
- Wire strippers
- Electrical tape
- Tape measure
- Heat shrink
- 12V relay
- Fuse tap and fuse
- Spotlight switch
- Cable connectors (spade connectors to the relay and switch, ring connection to the battery for example)
- Cable (appropriate gauge, red for power and black for earth/ground)
Wiring Kit or Harness
Many companies supply a wiring harness, or loom, with spotlights. These are excellent as they take out most of there guesswork concerning wiring (fuses, cable gauge and length, reliable connections). Many of them also include vehicle-specific components to connect directly to existing headlight and high beam circuits.
Buying such a suitable kit or harness saves a lot of time because you don’t necessarily need to connect a spotlight switch from the fuse box nor be too concerned about the amount of wiring you need to buy to complete the installation; the harness will be a simple way to carry out the work and eliminate almost all the guesswork.
If doing this without a kit or wiring harness, you’ll need to buy a 12V relay to control the spotlights as well as appropriate wiring and fuses. The beauty of a relay is that you do not need to use the full power required to power the spot lights to also power the switch. A lower-power signal wire can be run from the relay to switch the spotlights on and off instead, which is safer and more cheaper.
Relays are a pretty universal 12V accessory, and the numbers on the back- 30, 85, 86, and 87 (and 87a)- are an indication of this. It seems a little intimidating initially, but a relay is just a switch controlled by electricity. More info can be found here.
Find your fuse box and get the fuse diagram; you will need to find your high beam fuse. Fuse boxes are in the engine bay or under the dashboard.
Have a look in the engine bay for any cable grommets or holes that can be used to route the wiring for the spotlight switch. There will be no need to drill a new hole. While you’re at it, have a think about how you will route the wiring. An old coat hanger is a good tool to help feed wires through awkward areas.
Make sure your wiring is safely routed, secured, and insulated. The last thing you want is for any arcing or short-circuiting. Heat shrink and zip ties are useful here. Consult with or employ an expert if you are not confident in what you are doing.
The spotlights should specify how much current (in Amps) they draw, which will help determine what gauge (thickness) cable will be required for your spotlight wiring. The more powerful the spotlights, the more current they are likely to draw. There are many guides online with simple charts (like the one below) that can help.
- If you are working without a wiring kit or harness, draw up a wiring diagram. It will give you an idea of how much wiring you will need to run from the battery to the relay and the relay to the lights and to not incorrectly wire anything. Really, draw up a wiring diagram.
- Find a suitable location to mount the relay. Somewhere on the back of the engine bay near the battery is ideal (and is likely well away from moisture and heat). Don’t secure it yet.
- Disconnect the negative cable from the car battery’s negative (-) terminal.
- Run a red power wire from the positive (+) terminal – ideally through an appropriate fuse – to relay Pin 30.
- Route another red power wire from the spotlights around the side of the engine bay and connect it to relay Pin 87. The spotlights can be ground to the vehicle (using a black cable).
- Identify the fuse for the high beam and replace the fuse with your fuse tap (it might be necessary to drill a small hole in the fuse box to run the wire through for the fuse tap). Route a wire from the fuse tap, which will be powered on when the high beams are turned on, and connect it to relay Pin 86.
- On this part of the circuit, you need to install the switch to turn the spotlights on and off (as most aftermarket lights are not allowed to be used while driving on public roads). This allows the high beams to still be used without the spotlights). Find a suitable location in the cabin for the switch; the centre console or the within easy reach on the dashboard is a good bet (Note: most harnesses avoid this need to go into the fuse box by simply connecting directly to a high beam bulb’s plug).
- Ground the relay from Pin 85 somewhere on the vehicle body (an existing bolt in the firewall would be perfect). Secure the relay to the vehicle.
- Connect the negative cable to the battery again.
- Test your wiring circuit. Jump in your car, turn the spotlight switch on, then turn on your headlights and high beams. If the spotlights come on with your high beams (not your low beam), you’ve wired the circuit correctly.
- If the spotlights don’t turn on, don’t panic. Check all the ground connections first (you might need to sand off some paint or rust to ensure a good ground connection), and then check each connector to the relay. Have your wiring diagram handy. Turn the spotlight switch off to test if the spotlights also turn off. If they turn off, you’ve been successful in wiring up your spotlights and everything is connected correctly.
Can you hook up a light bar to high beam?
Yes, as it is an accessory just like spotlights it can be wired exactly the same. Some allowances might need to be made regarding wire gauge and fuses.
Can you wire a light bar without a relay?
Yes, but a relay is a cost-effective way to safely power an LED light bar, driving lights, or spot lights. It means you don’t need to run a thicker, more expensive power wire through the engine bay to the cabin and elsewhere; you can use cheaper, thinner wires to just control the relay signal.
How do you find high beam wire?
Your fuse box should come with a fuse diagram to identify which fuse is for which component on the car or ute. Most spotlight wiring kits utilise the actual high beam globe and plug directly into the back of the globe, saving you the need to splice into any wires.
Can you use a light bar as headlights?
No. Headlights (both low beam and high beam) are rigorously tested to meet ADR and registration requirements and, as a general rule, the existing headlight system should not be modified. Spotlights and light bars are an accessory and normally come with a caveat that restricts their use to private roads and property only.