4 Steps to Wire a Relay for LED lights

If you are driving at night frequently, an LED light bar on your vehicle is a great help! However, it can be challenging to create a relay for LED lights. To help you, we will share information and a step-by-step procedure on how to wire a relay for LED lights.

Understanding Relay

4 pin relay wiring diagram

Before proceeding to the tutorial, let us define what relay means first. A relay is an electrical switch. It allows the low-current switch controls the electricity’s flow from the high-current circuit. If you need to install LED lights with a high current, you must install a relay.

What will happen if there is no relay? If you installed a high-current LED light, your switch needs to handle the full current.

If it fails to handle the current, the switch may overheat, or the wires may melt. If this happens, the current you will be getting from the LED light will reduce. It may result in less bright light.

Inside a relay are an electromagnetic coil, a spring, and the contact. The spring keeps the contact at rest until a current goes through. On the other hand, the coil creates a magnetic field so that the contact will move to the opposite pin.

In a relay, you will find four points: 30, 87, 85, and 86. These points indicate how the wires should be connected and positioned. By connecting the wire to 30 and 85, you can create a switch for your light.

The prong 30 serves as the power source of the light tapped to the positive side of the battery. 87, on the other hand, is wired on the positive side of the LED light.

Once the relay has been installed, the switch will turn on automatically. It will prevent the battery’s current from directly flowing to your switch.

Without 85 and 86, there will be no magnetic force that will turn on your LED light. 85 is attached to the power source that controls the switch, while 86 is wired to the ground. Take note that these two are reversible.

Benefits of Relay

4 prong relay diagram

Enables a low-current circuit to control high current circuit

Controlling a high current circuit with a low current switch is one of the reasons many people wire a relay. A low current circuit cannot handle a high current circuit.

Connecting a low-current switch to a high-current battery will result in overheating. It can also melt the wires, affecting the LED light’s efficiency and brightness.

Wiring a relay is less costly than buying high-ampere wires and switches

As a basic principle, a high current circuit requires high current wires or switches. Wiring and switches that have high amperes may be expensive. Aside from being costly, they also take a lot of space. On the other hand, relays are less costly and available in compact sizes.

A single switch can control more than one circuit

You can use a single switch to control multiple circuits with a relay. It doesn’t matter if they have different current levels and voltage. The relays with immense power are used for main voltages. They are also utilized for other high-current switching applications.

Different Relay Applications in Vehicles

how to wire a relay

Installing simple applications of a relay is helpful to add LED lights to your vehicle. One of these applications is known as positive switching.

By connecting the switch to the positive terminal, positive switching happens. This kind of relay application is utilized for exterior lighting and brake lights. It is also helpful for an off-road light bar.

The negative switching’s trigger is attached to the negative terminal. Interior switches, trunk, door, and hatch are some of the negative triggers in your vehicle.

Negative switching is utilized for the lighting of the truck bed and under-hood. It is also applied in footwell lighting and some other interior lightings.

A switch-activated ignition override has valuable applications. It is recommended for those who like to open or close the light through the ignition or car’s power.

The benefit of this application is that your car’s light will turn off if you remove the key from the ignition. The same happens if the vehicle stops moving even the controller is on.

Wiring a 4-pin relay to LED light

4 pin relay diagram

Step 1: Prepare the materials needed to wire a relay for the LED lights

Before you proceed with wiring a relay, you need to prepare first all the materials you need. Make sure that you have the correct battery, switch, and relay. Once you have all of them, you can proceed to the next step.

Step 2: Find a place for the relay

The suitable place for a relay is dry and away from the heat of the other parts of the vehicle. Also, make sure that there is enough space not to be too difficult to install and connect the wires.

Step 3: Disable the terminals

Disable the terminals of the output wires. To do this, get the shorter section of the wires and separate each terminal by covering them with black tape.

It will prevent the terminals from touching each other. Once you have secured the terminal individually, cover the terminals together.,

Step 4: Tap the wires and secure them with electrical tape

Now that you have disabled the terminals, you can tap the wires. Connect the relay’s pin #30 to the battery’s positive terminal. For #87, connect it to the LED light’s positive side.

To control the LED light, connect #86 to the power source. You can choose the high beams or the reverse light. For the relay’s completion, connect #85 to a grounding.

You can interchange #85 and #86 if you want a unique way of wiring. Once done, check if the relay is working.

Wiring a 5-pin relay for LED light

relay wiring

Step 1: Connect the wires to the correct pins

First, connect #30 to the positive terminal of the battery. The #86 should be fastened to the ignition switch, while #87 should be wired to the network of the LED light.

87A must be connected to other light networks. The negative ends of the light networks you choose must be secured to the ground. For the switch, connect its positive end to #85, then ground its negative end.

With a 5-pin relay, you can turn the two light networks on and off. On the other hand, the ignition switch will help you choose which of the two light networks you want to use.

Step 2: Test if the relay is working

After connecting the wires, decide where to put the LED light switch. Make sure that it won’t interfere with the moving parts inside your car.

It can be dangerous if it limits the movement of your brake and steering wheel. It is also better to cover the wires so they won’t quickly wear out. Also, put some tapes or zip ties to excess cables.

Frequently Asked Questions

relay wiring diagram

Does the clicking sound from a relay indicate that it is faulty?

Yes. One of the indicators of a faulty relay is a clicking sound coming from it. It would be better if you checked the connection of the wires. It may be caused by loose wiring. Ensure that the cables are tightly secured to prevent any inconvenience on your part.

Can I still wire an LED light bar without a relay?

Yes, you can. However, you will need to have wire splicers instead. Aside from that, you will need to connect the battery with the fuse to prevent any sudden surge. Like with relay, you also need a switch, a power source, and an LED light bar.

What are the other types of relay?

Other relay types are high-voltage relays, electronic and semi-conductor relays. Timer and time-delay relays and thermal relays are also popular. You may also encounter overcurrent, differential, and frequency protection relays.

How does a relay work?

Once a voltage or a current goes through the coil, it will create magnetic energy. The magnetic field will move the contact that will activate the second circuit. When there is no power, the spring will move the contact to its original position. It will keep the second circuit off.

What are the differences between normally open and normally close relays?

The default of a normally open relay is in an open position when there is no contact between the circuits. When power passes through, it will move the first circuit to contact the second circuit.

It will allow the power to flow. The circuit is already completed for a normally close relay. The power will flow even the switch is not operated.


Relays for LED lights are helpful to prevent the wires and the switches from overheating. Although it may sound complicated, learning how to wire a relay for LED lights is easy.

You have to understand the concepts behind the relays. Also, familiarize the wires and points needed to be connected.

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