Automotive Relay Diagram! 4 & 5 Pin Relay Wiring Diagram

An automotive relay is an electrical switch, which turns ON and OFF by giving an electrical trigger. It is made up of two circuits, a coil and high amperage circuit. Each circuit has its pin numbers and wiring diagram.

Below is the complete guide about automotive relay diagrams such as four and five pin relay wiring diagram in easy to understand language.

Automotive Relay Diagram


The automotive relay wiring diagram is not complicated, it’s very easy. All you need to know is the basics of a car relay wiring diagram.

Here in this section, I am explaining the wiring diagram of the four and five-pin car relay. Stick with me, here I am giving you a little background about automotive relay terminals.

In the last century, Germany made an organization called DIN Standard. It stands for Deutsches Institut für Normung means the German Institute for Standardization. This national organization gives standard numbers (Known DIN Standard) to almost every field of technology, covering almost thirty thousand DIN Numbers. The DIN organization also gives a standard DIN code to motor vehicles.

The standard code for electrical terminals is known as DIN 72552 standard and is almost accepted throughout the world. DIN standardizes almost every terminal in an automobile with code. Here we will only discuss the relay’s terminals. Below is the wiring diagram of the four and five-pin car relay.


According to DIN 72552 Standard, each pin of a relay is numbered 85, 86, 30, 87, and 87a.

You need to know that a relay has two circuits, a coil circuit, and a high amperage circuit. In a relay 85 and 86 pins are considered coil circuit pins while 30, 87, and 87a pins are considered high amperage circuits.

Coil Circuit Pin Numbers

Usually, terminal -85 is given a ground power source and terminal +86 is given a hot power source, to make a complete circuit.

High Amperage Circuit Pin Numbers

Terminal 30 is considered to be a common terminal. 12-volt power comes to a relay through this terminal (we can say Power-In Wire).

And the second wire of high amperage circuit terminal 87 gets power out of the relay and sends it to the component (we can say Power out Wire).

There is also a third wire that comes in high amperage circuit of a 5 pin relay, which is called terminal 87a. It is the extra fifth terminal, which is not commonly used in automotive relays. It is used for circuits that need power when the relay is not activated.

4 Pin Relay Wiring Diagram

Car Relay Diagram


In four pin relay, there are four terminals, two terminals for coil circuits, and two for high amperage circuits. The coil circuit’s two terminals are 85 and 86, in which terminal 85 is the relay’s coil negative contact, and terminal 86 is the relay’s coil positive contact.

Similarly, the relay’s high amperage circuit’s two terminals are 30 and 87 in which terminal 30 is a common contact, which means it is an input contact, through this terminal the current goes into the relay whether that is positive or negative depends on the demand of power source.

And terminal 87 is normally open contact and closes when the relay is energized. It is also called an output terminal, which means the currents go out of the relay through this terminal to the component.

5 Pin Relay Wiring Diagram


In a five-pin relay, there are five terminals in which two terminals are for the coil circuit, and three terminals are for the high amperage circuit. The coil circuit’s two wires are terminals 85 and 86, in which terminal 85 is considered negative contact and terminal 86 is considered positive contact.

The five-pin relay’s high amperage circuit consists of three terminals 30, 87, and 87a. Terminal 30 is a common contact, the battery power comes through this terminal to the battery. Terminal 87 is an open contact and always stays open, closes when the relay is energized. The power goes out through this terminal to the component when the relay is energized.

Similarly, terminal 87a is a normally closed contact, and its contacts open when the relay is energized. It means, by default, it lets the current out without energizing the relay and stops the current when the relay is energized. It is used on applications where current is required when the relay is not energized.

4 Pin Relay Wiring Diagram For Lights


Terminal 86 wire of the relay’s coil circuit is connected to a hot power source, while terminal 85 is connected to a light switch, which is often a ground power source.

A fused wire comes from the fuse box to terminal 30 of the high amperage circuit, while the second terminal 87 is connected to the headlight. The coil circuit consumes almost 0.5 amp current, which is a not burden on the light switch, as a result, will not burn the light switch.

So, when the coil circuit is activated, the high amperage circuit will make the contact, and the current will directly flow from the fuse box’s battery connection to the lights and the light will illuminate.

4 Pin Relay Wiring Diagram For Horn


The relay coil circuit’s terminal 86 is connected to the battery positive power source, while terminal 85 is connected to the steering wheel horn pad, which is a ground power source. And
Relay’s high amperage circuit’s terminal 30 is connected with fused wire from the fuse box, while terminal 87 of the high amperage circuit is connected to the horn.


Whichever power source (positive or negative voltage) you give to the common terminal of the high amperage circuit of terminal 30. It will output that power to terminal 87 or 87a of a load wire.

For example, if you give terminal 30 hot power sources. In a de-energized state, the relay will power a hot power source to the 87a terminal while in an energizing state it will output a hot power source to terminal 87.

The same goes for ground power sources too.

A Good Way To Remember Relay Wiring Diagram

Some people have difficulties identifying pin numbers and terminals. I use a technique that helps me remember the pin terminals.

Usually, relay pin numbers are 30, 85, 86, and 87 (In 4 Pin Relay). Here, just for a while put terminal 30 aside then the remaining terminals will be 85, 86, and 87. Now at this time assume that 85 and 86 are starting numbers in the above terminals and also take the coil circuit of the relay as the initial circuit.

Now link in mind starting numbers represents the initial circuit. It means that terminals 85 and 86 represent the coil circuit. So, whenever you hear about the coil circuit remind yourself that It means terminal 85 and 86.

In this way, you can easily remember coil circuit pin numbers. Finally, the remaining two terminals 30 and 87 are for high amperage circuits. In which 30 terminal represents a common wire and 87 terminal is power out or load wire.

Related • How To Wire A 4 Pin Relay For Horn & Lights With Diagram: No More Confusion

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