Why do automobile horns tend to go off constantly during a vehicle fire or collision?
In: Engineering
The short answer is because of the simplicity of the circuit.
Like any electrical device it needs to be a complete circuit from the power source. So positive side of the battery to the horn, horn back to the negative side of the battery.
Now with horns, car manufacturers make things even simpler. They don’t have a return wire, they use the metal of the chassis as the return wire. So most horns just have a single positive wire coming to them. That single wire snakes from the horn, around the engine, in thru the harness, up the steering column, to a button switch in the steering wheel, down to the fuse box, and back to the positive battery terminal. Anywhere along that run, if the wire breaks and can contact another wire that has positive current, it will trigger the horn.
So if the insulation burns off the wires of the harness, that horn wire is going to contact positive power. If a crash causes the harness to smash and tear open that insulation coverage, the horn is going to activate.
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