Why do automobile horns tend to go off constantly during a vehicle fire or collision?
In: Engineering
couple possibilities.
Could be the heat melts the wire’s insulation, causing a short and making the horn sound off.
Could also be the driver slumped over the wheel pressing down on the horn with their chest
The constant note of the horn after an accident is indicative (especially in film/TV) that the driver is unconscious/slumped over the steering wheel (or, worse, trapped against it).
In addition to what has been noted, some manufacturers cascade events when a crash is detected:
horn, flashing lights, emergency services outreach (via OnStar, etc), and fuel pump shut off (the latter may be universal and required, not sure).
The idea is simply to attract attention in case the accident didn’t occur at a busy place. Not sure how prominent this is, but it’s something I noticed started quite a few years ago when I was a medic.
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.
Latest Answers