What You’ll Need Before You Start
Before diving into the installation, gather all your materials. Having everything ready will save you time and frustration. Here’s what you need:
- LED light bar
- 12V automotive relay (usually 40 amp)
- Inline fuse (matched to your light bar’s amperage)
- Light bar toggle switch or rocker switch
- 14-gauge automotive wire (red, black, and another color for the switch)
- Wire connectors (crimp connectors, ring terminals, or heat shrink butt connectors)
- Wire strippers and crimping tool
- Electrical tape or heat shrink tubing
- Multimeter (optional but helpful for testing)
Most light bars come with a light bar wiring harness that includes many of these components. However, building your own harness gives you more flexibility and helps you understand exactly how everything connects.
Understanding Your Light Bar Wiring Diagram
The key to a successful installation is understanding how electricity flows through your system. Think of it like a loop—power needs a complete path from the battery, through your components, and back to ground.
Here’s the basic flow: Power starts at your vehicle’s battery, travels through a fuse for light bar protection, goes to a relay for light bar control, then to your light bar switch, and finally reaches the light bar itself. The relay for light bar acts as an electronic gatekeeper, allowing high current to flow safely without overloading your switch.
The Role of Each Component
Your relay has four main terminals, usually numbered 30, 85, 86, and 87. Terminal 30 connects to your battery’s positive through a fuse. Terminal 87 sends power to your light bar. Terminals 85 and 86 control the relay—one goes to ground and the other connects to your switch. When you flip the switch, it activates the relay, which then allows full battery power to reach your light bar.
The fuse for light bar is your safety net. If something goes wrong and too much current flows, the fuse blows instead of your expensive light bar or vehicle wiring getting damaged. Always use a fuse rated slightly higher than your light bar’s normal draw but within safe limits.
Step-by-Step: How to Wire a Light Bar
Step 1: Mount Your Light Bar
Choose a secure location for your light bar—front bumper, roof rack, or grille are popular spots. Make sure the mounting bracket is tight and the light bar won’t move or vibrate loose while driving.
Step 2: Install Your Switch
Pick an accessible location inside your cabin for your light bar toggle switch. Many people use empty switch blanks on their dash or console. Drill a mounting hole if needed, then secure the switch in place.
Step 3: Connect the Relay
Find a good spot for your relay under the hood—somewhere dry and away from excessive heat. Here’s how to wire a light bar relay:
- Connect terminal 30 to your inline fuse, then run a wire with a ring terminal to the battery positive
- Connect terminal 87 to the positive wire of your light bar
- Connect terminal 85 to a ground point (vehicle chassis or battery negative)
- Connect terminal 86 to one side of your switch
Use ring terminals for secure connections and protect all connections with heat shrink tubing or electrical tape.
Step 4: Wire Your Switch
Your switch needs three connections. One wire goes to the relay (terminal 86), one connects to a constant power source (or ignition), and one goes to ground. If you want the light to work only when the vehicle is running, connect to ignition power. For operation anytime, use constant power from the fuse box.
Step 5: Complete Ground Connections
Run a black wire from the light bar’s negative terminal to a solid ground point—a bolt on the frame or directly to the battery negative terminal works great. Also ground terminal 85 on your relay and one terminal on your switch. Clean metal-to-metal contact is essential for reliable grounding.
| Wire Color | Purpose | Connection Points |
|---|---|---|
| Red | Positive Power | Battery → Fuse → Relay 30, Relay 87 → Light Bar |
| Black | Ground / Negative | Battery or Chassis → Relay 85, Light Bar Negative |
| Blue / Other | Switch Control | Switch → Relay 86 |
Tips for a Professional Installation
Keep your wiring neat by using zip ties to secure wires along existing harnesses. This prevents rubbing and potential damage. Always route wires away from hot engine parts and sharp edges.
Use proper gauge wire—14-gauge works for most light bars under 150 watts. Higher wattage lights may need 12-gauge wire. Undersized wire can overheat and create fire hazards.
If you’re installing multiple light bars, you can split the power from relay terminal 87 to feed several lights. Just make sure your relay and fuse are rated for the combined amperage.
Protect all connections from moisture. Heat shrink tubing with adhesive lining works better than electrical tape for long-term reliability. Water intrusion is a common cause of light bar failures.
Wrapping Up
Wiring a light bar switch is simple with a bit of patience. Using the LEDMIRCY LED Light Bar Kit makes installation even easier, with all components included for a hassle-free setup. You’ll enjoy neat, secure wiring, save time, and gain confidence for future vehicle upgrades. Always test connections and protect them from the elements.
Original price was: $89.99.$69.99Current price is: $69.99.
FAQs
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