how to wire a horn relay

How to Wire a Horn Relay: A Step-by-Step Guide

Wiring a horn relay is an essential skill for vehicle owners and enthusiasts alike. The horn serves as a crucial safety feature, alerting other drivers and pedestrians to your presence on the road. Whether you’re replacing a faulty horn or installing a new one, understanding the process of wiring a horn relay is paramount. In this comprehensive guide, we’ll take you through the step-by-step process of wiring a horn relay, ensuring your horn operates reliably and effectively.

Understanding the Horn Relay

A horn relay acts as a crucial intermediary between the horn button and the horn itself. It serves as a switch that controls the power flow to the horn circuit. The purpose of the relay is to allow a small amount of current from the horn button to trigger a larger current flow needed by the horn. This setup not only optimizes the use of space under the hood but also enhances safety and efficiency.

Essential Tools and Equipment

Before diving into the wiring process, gather the necessary tools and equipment. A wirecutter/stripper, multimeter, various gauges of wire, solderless butt connectors, a horn, and, most importantly, a horn relay are essential for this task. Having the right tools ensures a smooth and efficient wiring process.

Disconnecting and Testing the Original Horn

Begin by locating the original horn and disconnecting its wire. With the help of a multimeter, check for a 12-volt current in the wire while someone activates the horn. If no voltage is detected, ensure continuity between the battery’s negative terminal and the wire. This step is crucial to identify any underlying issues before proceeding.

Ensuring Safety: Disconnecting the Battery

Whenever working with electrical components, safety is paramount. Before you proceed further, disconnect the battery to prevent any accidental electrical shocks or damage.

Connecting the Relay’s Coil Circuit

The relay’s coil circuit plays a pivotal role in activating the horn. Connect the battery’s positive terminal to terminal 86 of the relay. This sets the stage for the relay to respond to the horn button’s activation.

Attaching the Horn Wire

Attach the horn wire to terminal 86 of the relay. Additionally, connect terminal 30 to terminal 85 to establish continuity. Ensuring proper connections guarantees the reliable operation of the horn.

Locating a Suitable Mounting Spot

Choosing the right location to mount the relay and horn is essential. Ideally, find an area close to the battery. This minimizes the length of wire required and optimizes the efficiency of the horn circuit.

Connecting the Power Source

To power the relay, connect one wire from the inline fuse holder to the battery’s positive terminal. Use an appropriate wire gauge, such as 10-gauge wire, and ensure a secure connection using a solderless ring terminal.

Connecting the Relay to the Horn

Attach the relay to the opposite end of the fuse holder and then connect it to terminal 30. Establish a connection between the horn and terminal 87. If your horn has two connectors, use a solderless connector and 10-gauge wire to attach the second connector to a metal part of the car.

Testing the Horn’s Functionality

Before concluding the wiring process, reconnect the battery. Give the horn a test honk to verify its functionality. If the horn sounds as expected, you’ve successfully wired the horn relay.

Wiring a 4-Pin Horn Relay

For those dealing with a 4-pin horn relay, the process is slightly different. Connect the battery’s positive terminal to terminal 86 for the coil circuit. Attach the horn wire to terminal 85. Terminal 30 is used for the high amperage circuit, while terminal 87 completes the horn circuit.

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Using a Radiator Fan Relay for More Power

For increased power requirements, consider using an 80A radiator fan relay instead of the standard 30A relay. Ensure the coil of the larger relay is actuated using a wire and the horn for compatibility.

Contactor Relay for Older Ford Vehicles

In some cases, older Ford vehicles may benefit from a contactor relay with a higher capacity of 150A. This relay is designed to handle more power, making it suitable for specific models.

Importance of Fuse Protection

Fuse protection is vital in electrical circuits, including horn relays. A fuse safeguards the relay and other components from excessive current, preventing potential damage.


Wiring a horn relay is a fundamental skill for every vehicle owner. A properly functioning horn enhances road safety and communication with other drivers. By following this step-by-step guide, you’ve gained the knowledge and confidence to wire a horn relay effectively. Remember to prioritize safety, use the appropriate tools, and ensure accurate connections for optimal results.


As long as the horn relay has energy, it can drain the battery. The relay drains the battery quicker when it is faulty.

Yes, the relay is essential when wiring the horn. The relay helps control the current to the horn’s circuit by delivering the connection to complete the circuit when you honk the horn.

Yes, remember that the fuse protects the relay from frying if there is too much current.

Signs of a blown relay include clicking sounds, no sound when honking the horn, and a burning smell.

Yes, you can upgrade to a larger relay, such as a radiator fan relay or a contactor relay for older Ford vehicles, to accommodate higher power requirements.

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