How to Wire Off-Road Lighting Using a Relay and Switch | BLIAUTO Professional Off-Road Lighting Installation Guide

In off-road driving, powerful auxiliary lighting is essential for conquering the night and challenging terrains. Whether it’s LED light bars, spotlights, or work lights, proper wiring not only affects brightness and stability but also directly impacts electrical safety and the service life of your equipment.

Using a relay and switch for wiring is the standard method for off-road lighting—it ensures the lamps receive stable power and allows flexible control via the switch. Today, BLIAUTO will explain in detail how to safely and efficiently complete this wiring process.

1. Why Off-Road Lighting Needs a Relay

The role of a relay in off-road lighting installation is indispensable:

Protects the switch and wiring

High-powered lamps draw large currents. If powered directly through the switch, the switch may burn out or the wiring may overheat. The relay allows the switch to control only a low-current signal, while the high current is supplied directly from the battery through the relay.

Reduces voltage drop

The relay shortens the length of the high-current circuit, reducing voltage loss through the switch, dashboard, or thin wires, resulting in brighter and more stable lighting.

Improves safety

Prevents high current from entering the cabin directly, reducing the risk of short circuits and overheating.

2. Common Materials Needed for Wiring

12V/24V relay (commonly 4-pin or 5-pin type)

Waterproof rocker switch / push-button switch

Lamp wiring harness (preferably with fuse)

Battery terminal connectors

Appropriate gauge wires (higher wattage lamps require thicker wires)

Wire terminals, electrical tape, heat shrink tubing

Multimeter (for checking voltage and verifying wiring)

3. Relay Wiring Principle

Using a common 4-pin relay as an example (pin numbering may vary slightly by brand):

Terminal 30: Connect to battery positive (via fuse protection)

Terminal 87: Connect to lamp positive

Terminal 85: Connect to switch output

Terminal 86: Connect to vehicle ground (or one side of the switch to positive and this terminal to negative)

How it works:

When the switch is turned on, terminals 85 and 86 form a control circuit that energizes the relay’s internal electromagnet, allowing terminals 30 and 87 to connect. This lets high current flow directly from the battery to the lamp.

4. Detailed Wiring Steps

Step 1: Determine mounting positions

Mount the relay close to the battery to facilitate high-current wiring and keep it away from heat and moisture.

Install the switch inside the cabin for easy access.

Step 2: Install the fuse

Add a suitable fuse (typically 1.25× the rated lamp current) between the battery positive and relay terminal 30.

Use a waterproof fuse holder if possible.

Step 3: Connect the lamp wiring

Lamp positive to relay terminal 87.

Lamp negative directly to vehicle ground or battery negative.

Step 4: Connect the switch wiring

Run a small-gauge wire from the ACC power (ignition-controlled) or constant power to the switch input; switch output to relay terminal 85.

Relay terminal 86 to ground.

Step 5: Test and secure

Use a multimeter to ensure no short circuits.

Lamp should turn on when the switch is “ON” and off when “OFF.”

Secure the wiring harness with zip ties to prevent vibration damage.

5. Installation Tips and Precautions

Prefer using pre-made wiring harness kits

BLIAUTO’s waterproof harnesses come with relay and fuse pre-installed, using heat-resistant wires to save you the hassle and risks of DIY wiring.

Choose waterproof switches and relays

Off-road environments often involve mud, water, and snow. Waterproof components last longer.

Ensure a solid ground

Clean and secure grounding points to ensure good metal-to-metal contact, avoiding flickering or failure to light.

Match wire gauge to load

For high-power LED light bars (e.g., over 200W), use at least 4 mm² copper wire.

Separate circuits for multiple lamps

Do not run multiple lamps through one relay—use separate relays for each group to ensure stability and safety.

6. Conclusion

Wiring off-road lighting through a relay and switch not only keeps the system running more reliably but also extends the lifespan of lamps and control components. For off-road enthusiasts, it’s an essential skill that enhances both safety and lighting performance.

As a professional off-road lighting solutions provider, BLIAUTO offers a wide range of LED light bars, spotlights, and waterproof relay harnesses compatible with various vehicle models—so you can face the night with confidence on every off-road journey.