How to Wire a 4 pin Relay | Step-by-Step Guide

Relays are the electrically operated switches that are widely being used in electronics circuits these days to control multiple operations. They work on the principle of electromagnetism to control the internal contacts.

Using relays, one can set a low current circuit to control high current circuits. This makes them equally beneficial for plenty of applications include LEDs, LED light bars, automotive, fog lights, and many other similar applications.

Two main types of relays being used are the 4 pins and 5 pin relay. The main difference between 4 pins and 5 pin relays is the number of circuits they can control at one time. Where 4 pins can control only one circuit, 5 Pin relay is capable of controlling power to more than one circuit at one time.

But, before we move on, do note that we can’t wire a 4 pin relay without knowing the applications. In other words, there is no single way to wire a 4 pin relay.

If you are interested in knowing how you can use a relay for fog lights, bar lights, and led lights, check out the linked articles.

Today we’ll discuss how to wire a 4 Pin relay and later on, I’ll briefly discuss how you can wire a relay for driving lights.

So, stick with article and enjoy your read!

Procedure to wire a 4 Pin Relay

The picture attached below represents the wiring diagram of a 4 pins relay. Later on, we’ll use this circuit diagram to wire a relay for driving lights.


For driving lights, you’ll have to connect the Pin 30 of the relay to the 12V battery with the help of a fuse. Here we are not connecting pin 30 with the battery directly; rather we are using a fuse. The reason behind this is that fuse protects us from overcurrents.

In case, we face some fault in the circuit of driving lights, then the fuse protects the burning of lights and other circuits from current overshoots.

Pin 85 of the relay is connected to the ground whereas Pins 87 and 86 are switching pins. With the help of this 4 pin relay, you can turn on the main beams bulbs of the driving light by switching the connections of the battery to either circuit connected with pin 86 or 87 of the relay.

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Why to use a 4 Pin relay for driving lights

The main purpose of installing this relay system is to keep dangerous voltages outside of your cabin or driving place. The high voltage your headlight going to need that is being delivered by the battery is kept inside the engine area with the help of a relay.

Basically, you can think relay as a switch that is controlled by another switch. The switch installed in the sitting cabin of the vehicle, on the front side of the driver is operating on very low voltage. See, this voltage isn’t high enough to harm either the driver or other electronic components. This switch is used to power the relay, which is basically an electromagnet. It’ll further control the high current circuit connected directly to the headlights.

This is how a low current circuit controls the high current circuit by keeping both the driver and car electronics safe and this is why we must use a relay in our headlights!

How to wire a relay for driving lights

Let’s briefly discuss the procedure of how to wire a relay for relay for driving lights.

1. Identify the wires of Headlights: The first step in order to wire the relay for the driving light is to identify the wires coming out of the driving lights. Normally, there are two wires connected to these lights out of which, one is the power wire, normally having a red color, and another one will be ground wire black in color.

2. Connect the wires: Now connect the negative ground wire to the body ground of the vehicle. Make sure, you make this connection right. Also, keep the positive power red wire away from any moving parts of the engine. We’ll connect this one with the relay in the next steps.

3. Connect the Relay: Here, we are using a 4 pin relay. The diagram on the side of this 4 pin relay represents everything about its connections. But still, if you don’t understand how to wire a 4 Pin relay, then let’s briefly discuss it here:

Each of the 4 pins of the relay has different numbers mentioned on it that you’ll probably see on the one you have recently brought. These include Pins 87, 86, 85, and 30.

We will connect the positive red wire coming from the front lights of the vehicle; we talked about earlier, to pin number 87 of the relay. The pin 85 of the relay will be connected to the body ground of the vehicle.

The Pin 86 is the wire that’ll be connected to a button or switch that is going to be operated by the driver while driving the vehicle.

Lastly, pin 30 of the relay which is still to connect is what’ll be powering the relay itself. It means, we’ll connect it with the 12V battery installed in the vehicle with the help of a fuse. But, what’s the purpose of installing the fuse here?

Here installing the fuse is compulsory as it protects us from large current overshoots. It can happen if there is a short-circuit in our setup. So pin 30 basically powers the relay and fuse for the overall protection.

For better understanding, we have presented the connections of a 4 pin relay for installing vehicles lights in tabular form.

Pin Number Connection
87  Positive of front lights
86 Acc on switch
85 Ground
30 Battery Connection through Fuse

These are the steps that you should follow to connect your relay for driving lights. But, what about reverse lights, Can we connect them in a similar way? Let’s find out that also!

How to wire a relay for reverse lights

For wiring the relay for reverse lights, the same procedure is used as explained above. It’s nearly the same for connecting the wiring relay for the front lights of the vehicle. The only difference is that pin 87 of the relay is connected to the positive of reverse lights.

We’ve presented the connections of the relay in tabular form for reverse lights to make them easy for you to understand without reading the whole section above!

Pin Number Connections
87 Positive connection from reverse lights
86 Acc on Switch
85 Ground
30 12V connection from battery through  fuse

Final Thoughts!

This is how you can wire a 4 pin relay for driving lights and reverse lights. Make sure you carefully follow the guide and connect the right pin to the right spot. Otherwise, you’ll not only be able to turn on your headlights properly but can lose the relay as well!

Key takeaway from this article is that 4 pin relays are wired differently for different applications. There are no set criteria that you can follow. So, look for your application and wire the relay accordingly!

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