Horn · relay · horn button
Car horn relay wiring diagram
A pair of horns draws 8–10 A, more than the horn button and the clock spring in the steering wheel can carry. So the button only grounds a relay coil, and the relay feeds the horns. Here is the circuit.
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The circuit
- Battery + → fuse (15 A for two horns) → relay 30; 87 → horns → ground.
- Relay 86 → permanent + or switched + (the horn often works with the ignition off).
- Relay 85 → horn button, which connects it to ground through the steering column.
Horn clicks but does not sound
A relay that clicks means the button and the coil work. The fault is on the power side: a blown fuse on 30, a bad horn ground, or a horn too weak from voltage drop on a long thin wire. In the simulator, click the horn wire to see the voltage that reaches it.
Build it in WireForge
- Drag in Battery, Fuse, Relay, two Horn devices, a momentary Switch (the horn button) and Ground.
- Wire 30 and 87 to the horns, 86 to +, 85 through the button to ground.
- Simulate and hold the button: the relay pulls in and both horns sound.
Questions
Does a horn need a relay?
Aftermarket twin horns do. Without one, the full horn current flows through the button and the clock spring, which overheat.
Which horn terminal is ground?
Many horns have one terminal and ground through the bracket; on two-terminal horns either one can go to ground.
What fuse for car horns?
One horn about 4–5 A: a 10 A fuse. Two horns: 15 A.
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