Negative Switched Relays for Spotlights: Understanding and Wiring

Guidance for Vehicles with Negative, Positive, and Dual-Switched High Beam Circuits

Introduction

When fitting spotlights (driving lights) to modern vehicles, it’s important to understand how the vehicle’s headlight circuits are switched. Some vehicles, such as certain Toyota Hilux and Nissan Navara models, use negative and possitive switching for the high beam. Others may use a combination of positive and or negative switching. Incorrect wiring can lead to malfunctioning spotlights or even damage to the vehicle’s electrical system. This guide explains negative switched relays, how to identify your vehicle’s system, and how to wire spotlights safely.

What is a Negative Switched Relay?

In a standard (positive switched) circuit, the head light supplies 12V positive power to the relay when activated. In a negative switched system, the head light connection completes the circuit by providing a ground (negative) connection instead. This means the high beam circuit is live (12V) all the time or sometimes with lights on only(all lights low and high), and the switch connects in between light output and relay to activate the lights. Many Japanese vehicles use this system.

Spotlight Wiring: Why It Matters

If you connect a spotlight relay expecting a positive trigger, but your vehicle uses negative switching, the relay will not operate as intended. In some vehicles, both positive and negative signals are present: positive is supplied when the headlights are on, and negative is supplied only when the high beam is on. This dual-switching requires careful wiring to ensure correct operation.

How to Identify Your Vehicle’s Switching System

Test the high beam wire: Use a multimeter to check the voltage at the high beam headlight wire:
If the wire reads 0V when high beam is off and 12V when high beam is on, it’s positive switched.
If the wire reads 12V when high beam is off and 0V (ground) when high beam is on, it’s negative switched.
Check for dual switching: Some vehicles supply both a positive and a negative signal depending on the state of the lights. Refer to your vehicle’s wiring diagram or test both wires with a multimeter.

Wiring a Relay for Negative Switched High Beams

To wire spotlights using a relay in a negative switched system, follow these steps:

Relay Pinout (Standard 4-Pin Relay):
Pin 30: Power input from battery (fused)
Pin 87: Output to spotlights
Pin 86: Trigger from high beam circuit (negative switched wire)
Pin 85: Connect to a switched 12V positive source (such as from the headlight circuit)
Connect Pin 86 to the high beam negative trigger wire. When the high beam is switched on, this wire will go to ground, activating the relay.
Connect Pin 85 to a positive 12V source that is only live when the headlights are on. This prevents the relay from being triggered accidentally when the high beams are not in use.
Connect Pin 30 to the battery positive through a suitable fuse.
Connect Pin 87 to the positive input of the spotlights.
Connect the spotlight ground directly to the chassis or battery negative terminal(not the same wire as relay).

Wiring for Dual Switched Systems

For vehicles with both positive and negative switching (where one wire provides positive when headlights are on, and another wire provides negative when high beam is on), you may need to use both signals:

Use the positive wire to provide power to the relay coil (Pin 85), and the negative high beam wire to ground the other side of the relay coil (Pin 86). This ensures the relay only activates when both headlights are on and high beam is engaged.

Safety and Tips

Always fuse the power supply to your spotlights close to the battery to prevent electrical fires.
Double-check all connections and test the system before fully securing the wiring.
If unsure, consult your vehicle’s wiring diagram or seek professional advice, especially for vehicles with complex or computer-controlled lighting systems.
Be mindful that incorrect wiring can trigger warning lights or lead to improper functioning of your headlights or spotlights.

Conclusion

Understanding whether your vehicle uses positive, negative, or dual switching for the high beam circuit is crucial for safely and effectively wiring spotlights. Taking the time to test and wire correctly will ensure reliable operation and avoid damage to your vehicle. This is particularly relevant for popular models like the Toyota Hilux and Nissan Navara, where negative or dual switching is common.

This is a brief guide only and we take no responsibility for your own wiring, if you are unsure get your lights wired up by an experienced installer.