Adding an aftermarket air horn to your vehicle significantly boosts its audible presence, enhancing safety and adding a touch of personality. However, directly connecting a powerful air horn to your vehicle's existing horn circuit can overload the system and potentially damage it. That's where a relay comes in. This guide provides a simple, step-by-step explanation of how to wire an aftermarket air horn relay, perfect for beginners.
Why Use a Relay?
Before diving into the wiring, let's understand why a relay is crucial. Your vehicle's horn circuit is designed for a specific amperage. High-output aftermarket air horns often draw more current than your factory horn circuit can handle. A relay acts as a switch, allowing the low-current signal from your steering wheel button to control a much higher-current circuit powering the air horn. This protects your vehicle's electrical system from damage.
What You'll Need:
- Aftermarket Air Horn: Your chosen high-decibel horn system.
- Relay: A 12V automotive relay (typically a 30/40 amp relay is sufficient). Ensure the relay's amperage rating is higher than your air horn's.
- Wiring Harness: This will include sufficient length wires of appropriate gauge. Use a thicker gauge wire for the power and ground connections to the air horn, as these carry higher current.
- Inline Fuse: A fuse is vital for protecting your circuit. Select a fuse with an amperage rating slightly higher than the air horn’s draw.
- Wire Connectors/Crimps: For secure and waterproof connections.
- Electrical Tape: For insulating connections and preventing shorts.
- Screwdriver(s): To connect the relay and potentially the horn itself.
Step-by-Step Wiring Instructions:
This explanation assumes a standard 4-pin relay. The pin numbers may vary slightly depending on the relay model, so double-check your relay's diagram!
1. Understanding the Relay:
Most relays have a diagram printed on them. However, they generally function as follows:
- 85 (Relay Coil -): Connects to ground.
- 86 (Relay Coil +): Connects to the vehicle’s horn wire.
- 30 (Power): Connects to the positive (+) battery terminal (or a fused positive source).
- 87 (Output): Connects to the positive (+) side of the air horn.
2. Locate the Vehicle's Horn Wire:
This wire is typically located near the steering wheel. It's usually a thin gauge wire, and a simple way to identify it is to temporarily disconnect your existing horn. The wire that stops the horn from working when disconnected is your horn wire. Use a multimeter or a test light to ensure this wire only has power when the horn button is pressed.
3. Wire the Relay:
- Connect 85 (Relay Coil -) to ground: Use a wire to connect this pin to a clean metal ground point on your vehicle's chassis.
- Connect 86 (Relay Coil +) to the vehicle's horn wire: Carefully connect this pin to the wire you identified in step 2 using a crimp connector. If your relay has a high current, you can also use a diode here to reduce voltage spikes from the coil.
- Connect 30 (Power) to the battery's positive terminal: Run a thick gauge wire from the positive (+) battery terminal to the 30 pin. Include an inline fuse close to the battery for safety.
- Connect 87 (Output) to the positive (+) side of the air horn: Run another thick gauge wire from the 87 pin to the positive terminal of your air horn.
4. Ground the Air Horn:
Connect a heavy-gauge wire from the negative (-) terminal of the air horn to a solid ground point on the vehicle's chassis.
5. Install the Air Horn:
Mount the air horn securely in a suitable location, ensuring that it won't obstruct airflow or be subjected to excessive moisture.
6. Test the System:
Once everything is connected, turn on your ignition and press the horn button. Your aftermarket air horn should sound! If it doesn't, carefully double-check all your connections.
Troubleshooting:
- No sound: Check all connections, fuses, and ensure the relay is functioning correctly.
- Weak sound: Check for voltage drops in wiring or an undersized fuse or relay.
- Constant sound: The 86 (Relay Coil +) might be grounded or shorted.
Remember, safety is paramount. If you're uncomfortable working with car electrical systems, it's always best to consult a professional. By following these simple steps, you can enjoy the added safety and auditory boost of an aftermarket air horn, all while keeping your vehicle's electrical system safe.
