dual horn diagram

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A dual horn diagram shows the electrical configuration for two horns operating together to provide higher sound output for vehicle warning signals and attention-getting functions. The diagram illustrates parallel connection of two horn units (typically one high-pitch tone 400-500 Hz and one low-pitch tone 200-300 Hz) to a common relay and power supply. The horn relay receives its control signal from the steering wheel horn pad switch through a low-current steering column connection. This relay arrangement isolates the horn pad switch (carrying only milliamps) from the high-current horn circuit (drawing 10-20 amps total), preventing switch contact erosion and enabling convenient steering-wheel-mounted switching. The diagram shows the relay coil connection to ignition battery voltage and horn pad switch, with the relay contacts carrying horn power directly from the battery. Each horn includes a adjustable resonator chamber tuning for optimal frequency response. Modern dual horn diagrams may include electronic horns, variable tone selection via microcontroller, or integration with vehicle security and communication systems. Understanding dual horn wiring enables horn troubleshooting, aftermarket horn installation, and replacement of failed relay or switch components.

Dual horns — one high-tone and one low-tone — produce a richer, more attention-grabbing sound than a single horn, and are a common upgrade on passenger cars and motorcycles. Because two horns together draw more current than a single unit, using a relay to handle the load is strongly recommended to protect the factory horn button circuit and wiring. CircuitDiagramMaker.com lets you draw and share a complete dual horn relay wiring diagram free online without any software to install.

How to wire dual horn diagram

Select mounting locations for both horns Mount the high-tone horn slightly apart from the low-tone horn for best acoustic projection. The front bumper area or behind the grille is standard. Ensure both horns face forward and are protected from direct water splash — water ingress into the back of an electromagnetic horn causes corrosion and premature failure.
Run a relay close to the horns Mount a standard automotive relay (30 A, 12 V) in the engine bay near the horn mounting positions. A short high-current cable between relay and horns reduces voltage drop. Long runs of undersized cable between relay and horns reduce horn output noticeably.
Wire relay coil to horn button Connect relay coil terminal 86 to a switched ignition positive supply. Connect relay coil terminal 85 to the horn button signal wire at the steering column. When the horn button grounds terminal 85, the coil energises and the relay pulls in. This keeps high current out of the steering column wiring.
Connect relay output to both horns Run a 10 A-rated wire from relay output terminal 87 to the positive terminal of both horns, wired in parallel. The relay common terminal 30 connects to a fused permanent battery positive. Use a 15 A fuse in this feed to protect the relay output and horn wiring.
Earth both horns to body Connect the negative terminal of both horns to a solid vehicle body earth point, not a painted surface. A bad horn earth is the most common reason new dual horn installations sound weak. Use a self-tapping screw into bare metal and apply a dab of anti-corrosion grease over the connection.
Test sound level and tone Sound the horn and confirm both tones are audible. A chord of two tones should be clearly distinguishable. If only one horn sounds, check the connection to the other and verify the positive terminal is receiving relay output voltage. If both horns sound the same pitch, confirm you fitted a high-tone and low-tone pair.

Frequently asked questions

Why do vehicles use two horns instead of one?

Two-horn systems use a high-tone and a low-tone horn to produce a chord, which is louder and more attention-getting than a single tone. The combination produces a fuller, more authoritative sound. Fleet vehicles, trucks, and performance cars commonly use dual horns. The sound pressure levels of the two horns combine for better penetration in traffic.

Do both horns in a dual horn system run off the same relay?

Yes, in a standard dual horn wiring diagram, both horns are wired in parallel to the output of a single relay. The relay coil is triggered by the horn button, which only needs to switch the small relay coil current rather than the full motor current of two horns. This prevents burning the horn button contacts.

Can I wire dual horns without a relay?

Technically yes if the horn button contacts are rated for the combined horn current, but it is not recommended. Most steering wheel horn buttons are rated for only 5–10 A. Two horns can draw 8–15 A total. Running this through the steering column contacts causes overheating, premature wear, and clock spring failure on vehicles with airbags.

What voltage do automotive horns use?

Standard automotive horns are designed for 12 V DC. Some heavy vehicles use 24 V horns. Fitting a 12 V horn on a 24 V system burns out the horn in seconds. A dual horn kit sold for passenger cars is 12 V — confirm your vehicle system voltage before purchasing.

How do I adjust the tone of a dual horn?

Many electromagnetic horns have a small adjustment screw on the back of the horn body, accessed through a slot. Turning it adjusts the armature air gap, which changes the resonant frequency and therefore the pitch. Adjust in small increments — over-adjusting causes the horn to stop sounding rather than change pitch.

How do I wire dual horns with a relay?

For a dual horn relay wiring diagram, connect relay pin 86 (coil positive) to the factory horn wire at the horn button so pressing the horn energises the relay coil, and connect pin 85 (coil negative) to chassis ground. Run a fused battery positive feed to relay pin 30, then connect relay pin 87 (normally open) to both horn positive terminals wired in parallel; ground both horns to the chassis. This arrangement means the relay contacts — not the horn button — carry the full current for both horns, protecting the steering column wiring from overload. A 30 A relay and a 20–25 A inline fuse on the battery feed are typically sufficient for a standard dual-horn kit.

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