Do you need a relay for a light bar?
High-performance lighting systems, like lightbars, are a key component of any emergency vehicle, from police cars to ambulances and fire trucks. This powerful illumination is crucial for visibility and safety in high-stakes situations. But do you need a relay for your light bar?
Absolutely! If your light bar has a significant amp draw, a relay switch is a must. Emergency vehicles often use several electronic systems at once, and a relay helps manage that power load efficiently. This relay not only boosts your light bar’s performance but also protects your vehicle’s electrical system without compromising safety standards.
At Australian Warning Systems, we supply and install a range of heavy-duty vehicle lighting solutions. Here, we explain what a relay switch is, its benefits, and how to wire it to a light bar. Keep reading to learn why this device is essential for emergency fleets.
What is a light bar relay and how does it work?
A relay is an electrical switch that allows a low-current signal to control a high-current circuit, like a light bar. It acts as an intermediary between your vehicle’s battery and the light bar, supporting safe and efficient power delivery.
For instance, the dashboard switch doesn’t directly power your headlights. Instead, it triggers a low-current signal to the relay, which then engages the high-current circuit to illuminate the lights.
A relay consists of four key parts: a coil, a switch, a common terminal, and a normally open terminal.
When a low-current signal energises the coil, it generates a magnetic field that closes the switch. This action connects the common terminal to the normally open terminal, enabling current to flow through the high-current circuit.
Once the coil is no longer energised, the switch opens, cutting off the flow of electricity and breaking the circuit.
Why do you need a relay for a light bar?
When your light bar has a large amp draw, a relay steps in to protect your electrical system. This keeps standard switches from overheating, preventing wire damage and ensuring your light bar gets all the power it needs.
For emergency vehicles, which run multiple electrical devices at once, a relay is even more critical. It helps balance the power demands of the light bar without frying circuits or burning out switches.
Without a relay, the full electrical current would flow through the switch, increasing the chances of overheating or even system failure—a disaster in any situation, but especially in emergencies when every second counts.
Let’s take a closer look at why you need a relay for a light bar:
Safeguard your vehicle’s electrical system
Emergency vehicles are packed with electrical devices, and light bars are particularly power intensive – especially if they have multiple LEDs.
Without a relay, this lighting can overload the switch and wiring, leading to overheating, blown fuses, and even fire. Ultimately, this could mean costly repairs or, worse, a vehicle sidelined during a critical emergency.
A relay manages those high currents safely, curbing the risk of electrical failure. It takes the heavy load off your control switch, ensuring the light bar operates smoothly without putting unnecessary stress on your vehicle’s electrical system.
Boost your light bar’s longevity
Emergency vehicle light bars endure frequent use and long hours of operation, so durability is key.
By incorporating a relay, the switch only needs to manage a small current to trigger the relay, rather than handling the full power load of the light bar.
This drastically reduces wear and tear on your switches, extending their lifespan and enhancing the reliability of your entire setup. It’s a simple way to keep your lights shining brighter for longer.
Ensure a reliable power supply
In emergency scenarios, clear visibility can make all the difference. A relay guarantees that your light bar gets a stable, uninterrupted power supply, even with multiple systems running in your vehicle.
Without one, you risk power dips that lead to flickering or inconsistent performance—something no emergency fleet can afford.
When every second counts, you need your emergency lights to work flawlessly. A relay ensures they deliver while staying within the vehicle’s electrical capacity.
Enjoy a more flexible setup
With a relay, you can use various switch types, including toggle, rocker, push buttons, or remote controls.
You can also wire your light bar into different circuits—such as high beams, low beams, or fog lights—allowing you to activate it with specific triggers.
This setup gives you maximum control over your light bar’s operation for unrivalled performance and convenience.
How to wire a light bar with a relay
If you’re planning to wire a light bar using a 4-pin relay, the setup revolves around four key terminals: 85, 86, 87, and 30. Terminal 30 serves as your main power supply, while terminal 86 acts as the control switch for that power. Terminal 85 is responsible for grounding, and terminal 87 connects to the device—in this case, your light bar.
Once the switch at terminal 86 is activated, the circuit closes. This allows power to flow from terminal 30 directly to terminal 87, illuminating your light bar.
For those using a wiring harness, these connections may already be in place. However, if you want your light bar to come on with another action, like when you flick on your high beams, you’ll need to customise the installation and wire the switch yourself.
While it’s always wise to consult an auto electrician for jobs like this, here’s a general guide to help you understand the process:
1. Select the right relay
To ensure everything runs smoothly, pick a relay that’s in sync with your vehicle’s electrical setup—whether it’s 12V or 24V, depending on your ride. You also need to make sure the relay is rated to meet the current demands of your light bar.
2. Connect the power source
Connect the prong labelled 30 to the positive terminal of your battery, or, if you prefer, to a power source that only activates when the vehicle’s ignition is switched on.
Remember to install a fuse between the battery and the relay to prevent the circuit from overloading.
3. Setup the switch
Wire prong 86 to your switch, which controls the low-current circuit. This clever setup activates the relay, allowing the high-current flow to power up your light bar when you need it.
4. Wire the LED light bar
Attach the prong labelled 87 to the positive wire of your light bar, and connect the prong marked 85 to a suitable ground. Once you hit the switch, the relay will kick in, sending power straight to the light bar to light it up.
5. Test the installation
After finishing the wiring, try turning on the light bar to make sure everything is working as expected. The relay should engage when the switch is activated, and the light bar should illuminate steadily without any flickering or dimming issues.
Explore LED light bars and spotlights for emergency vehicles
So, do you need a relay for a light bar? For emergency vehicles, the answer is usually yes. A relay keeps your electrical system running smoothly, protects critical components, and ensures your lights are reliable in high-pressure situations.
At Australian Warning Systems, we offer a diverse range of light bars for various applications. Every product is engineered for maximum safety, performance, and durability—so you can take on the road with confidence knowing you’re backed by the best.
Want to learn more? Contact our expert team at 03 9796 5880 or email [email protected]. We proudly supply LED lighting solutions across Australia.