If you want your off-road lights to turn on and off with your headlights, you’ll need to tap into the electrical circuit of your headlights. In this guide, we’ll walk you through exactly how to do that using a relay to safely integrate your off-road lighting into your vehicle’s electrical system.
How to Tap Into Your Headlight – VIDEO
Tools & Equipment
For this demo, we’ll be using a Blue Sea Blade Fuse Block. There are several types of fuse blocks available, including models from Progressive Dynamics, Blue Sea Safety Hub, and Tiger Expedition UFO 200. While the specifics may vary, the connection method is essentially the same. You’ll also need a distribution hub—such as the Victron Lynx Distributor—to bring power from the battery, but we’re going to focus on the connections to the outlets for now.
Safety First
Before starting, always make sure your power is off. In this demo, we’ve already pulled the fuse from the fuse block to ensure there’s no power running through the wires while we work.
How a Relay Works in This Setup
A relay is an electrically controlled switch that allows a small amount of power (from the headlight circuit) to control a larger electrical load (the off-road lights). Instead of drawing power directly from the headlight circuit—which isn’t designed to handle the extra load—a relay ensures that your off-road lights receive power from a dedicated fuse block while still turning on and off with your headlights.
Identifying the Headlight Circuit
To tap into your headlight circuit:
- Locate the wiring at the back of your headlights.
- Identify the positive wire that supplies power to the headlight.
- Use a Posi-Tap connector to safely tap into this wire without cutting or stripping it.
Connecting the Relay
Once you’ve found the correct wire:
- Connect one side of the Posi-Tap to the positive headlight wire.
- Attach a signal wire to the other end of the Posi-Tap.
- Run this signal wire to the relay’s signal terminal.
- Wire the relay’s power input to the fuse block, ensuring it’s fused appropriately.
- Connect the relay’s output to your off-road lights.
- Ground the relay properly.
Why You Need a Relay (And Not Just a Direct Tap)
You cannot power your off-road lights directly from the headlight circuit. The headlight circuit is designed to power only the factory headlights and isn’t sized to handle the additional load of high-powered off-road lighting. Instead, the relay acts as a switch, using the headlight circuit only as a control signal while the main power for your off-road lights comes from a dedicated source.
Final Steps
Once everything is wired correctly:
- Turn your headlights on—your off-road lights should also turn on.
- Turn your headlights off—your off-road lights should shut off.
This setup ensures that your off-road lighting functions seamlessly with your factory headlights without overloading your vehicle’s electrical system.
Wrapping Up
Using a relay and a Posi-Tap, you can safely integrate your off-road lights with your vehicle’s headlights. While tapping into a factory wire does cause some minor intrusion, this method is commonly used in vehicle modifications and is considered a reliable way to achieve this functionality.
In our next guide, we’ll shift focus to interior lighting and dimmers, including why two-way dimmers don’t work as expected. Stay tuned!
