How to Wire a 4 Pin Relay (Step-by-Step Guide)

By definition, a relay is an electricity-operated switch. It is used in electronic circuits to regulate and control multiple operations. With the help of a relay, you can control a high current circuit via the setup of a low current circuit. Four-pin relays are commonly used in the application of fog lights, LED lights, and automotive electronics.

Wiring a four-pin relay is a simple three-step process:

  • Connect a 12V battery to Pin 30 of the relay via fuse
  • Connect Pin 85 to the ground
  • Pin 86 and Pin 87 are to be used as switching pins

Procedure to Wire a Four Pin Relay?

Although wiring a four-pin relay seems like a complex and technical job, trust me it is quite an easy task that you can manage on your own. So, let’s get started to wire a four-pin relay.

pin layout circuit diagram

To wire a four-pin relay for driving lights, the first step is to use a fuse to connect the 12V battery to the Pin 30 of the four-pin relay. The reason why we connect the relay via a fuse instead of directly establishing a connection with the battery is to avoid any over currents. Thus, connecting via a fuse is a much safer and more practical option. In the event of any issues in the driving light circuit, the fuse will protect the lights and circuits from burning due to intolerable levels of current.

Keep in mind that Pin 86 and Pin 87 of the relay are switching pins and Pin 85 should be connected to the ground. Using this four-pin relay you can switch on the main beams’ lights of the driving light by alternating the battery connections with either Pin 86 or Pin 87 in the relay.

Why Use a Four Pin Relay for Driving Lights?

There are a variety of different kinds of relays including four-pin relays and five-pin relays and so much more. But have you ever wondered why we often use a four-pin relay for driving lights?

To steer clear from harmful and damaging voltage outside your driving zone or cabin it is best to put in place a four-pin relay system. The relay helps contain the high voltages required by the headlights and delivered by the battery within the engine area. Thus, the relay acts as a safe closure space for all the raging voltages and currents.

In simple terms, if you observe the workings of a relay, it is kind of like a switch that is controlled by another switch. The switches installed in the driver’s seating area of the vehicle or the interior of a cabin work on extremely low voltages. This low voltage will not be powerful enough to cause any harm to the driver of the vehicle and its components. Thus, this switch being an electromagnet revs up the power of the relay to control the headlight circuits powered by high voltages of current.

Thus, it is evident how a low current circuit takes control of a high current circuit intending to stabilize the safety and security needs within a vehicle. Hence, it is proved that the relay which facilitates this process is Indeed a much-needed intervention to avoid any disasters.

How to Wire a Relay for Driving Lights?

If you are keen to learn more about how to wire a relay for driving lights. This step-by-step guide will help guide you on how to wire a relay for driving lights. It is a simple three-step process:

  • Correctly locate the headlight wires
  • Establish a connection to the wires
  • Get your Four-pin relay connected

Step 1- Correctly Locate the Headlight Wires

locating the headlight wires
Video | Rocky X TV

Firstly, find out the wires that come out from the driving lights. For easy identification purposes, the power wire will be colored in red, and the ground wire will be colored in black. Make sure to identify the two wires correctly right at the beginning to avoid any mishaps or accidents later on.

Step 2- Establish a Connection to the Wires

establishing connection to wires
Video | Rocky X TV

The ground of the vehicle body should be connected to the negative ground wire. Do not bring the red wire closer to any moving parts of the engine to avoid any accidents or issues.

Step 3- Get Your Four Pin Relay Connected

connecting the pin relay
Video | Rocky X TV

Now you need to get your four-pin relay connected.

The positive red wire will be connected to pin 87 of the relay and pin 85 of the relay will be connected to the vehicle body as mentioned under step 2.

Pin 86 will be the wire that connects to the switch to be operated by the driver while driving the vehicle. And finally, the 12V battery installed in the vehicle or cabin will be connected to pin 30 of the relay.

Please note that you need to connect the 12V battery to the Pin 30 of the relay using a fuse. Do not connect it directly.

The reason for using a fuse as a medium is to ensure that there is no large damage caused in case of electrocution due to high voltages of current flowing which may happen due to an instance of short-circuit in your four-pin relay setup. Now your four-pin relay is all set up and ready to use. (1)

How to Wire a Relay for Reverse Lights?

without and with relay diagram

Reverse lights can also be wired following the same procedure as outlined above with one exception. For reverse lights, the only change to be made in the relay is that the positive of reverse lights should be connected to Pin 87.

Just to give a quick recap of wiring the relay for reverse lights: Pin 85 is connected to the ground. Pin 87 is connected to the positive connection from reverse lights. Pin 86 is the wire that connects to the switch which will be operated by the driver of the vehicle. And finally, Pin 30 of the relays is to be connected to the 12V battery of the vehicle via the help of a fuse.

Once again, do not connect the Pin 30 directly to the 12V battery as it can be dangerous in the event of a short circuit that can harm you and the vehicle. Simply follow these instructions and you can set up a relay for reverse lights in no time.

Wrapping Up

Setting up four-pin relays for driving and reverse lights is quite an easy task that you can manage on your own without technical help if you follow our highly comprehensive and detailed step-by-step guide. Hope you found this guide useful in assisting you with setting up a four-pin relay at home. (2)

Take a look at some of our related articles below.

(1) electrocution –
(2) technical help –

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About Sam Orlovsky

b1d87d2ee85af3e51479df87928bdc88?s=90&d=mm&r=gCertifications: B.E.E.
Education: University Of Denver - Electric Engineering
Lives In: Denver Colorado

Electrical engineering is my passion, and I’ve been in the industry for over 20 years. This gives me a unique ability to give you expert home improvement and DIY recommendations. I’m not only an electrician, but I also like machinery and anything to do with carpentry. One of my career paths started as a general handyman, so I also have a lot of experience with home improvement I love to share.

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