Car Horns
Ford F-150
Grand Prix GT

What would cause the horn to start blowing by itself and cannot be turned off with the key in the ignition switch?


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Wiki User
2005-11-14 22:28:12
2005-11-14 22:28:12

The horn switch or relay.Your ignition switch does not power up the horn switch or relay,the switch and relay have constant power to them at all times as long as the battery is hooked up.I would start with checking the relay and then go to the switch. Also, check the wire under the steering wheel cover. If this wire is gounding out it will case the horn to blow Probably moisture in the horn circuit. The horn is always hot. The circuit is made by completing a ground. This way, several different circuits can energize the horn easily, i.e., the car's alarm, which it may or may not have. Moisture bridging a certain wire/terminal with the chassis will make the horn blow. Brake lights are probably wired the same way. They can come on without pressing the pedal. Completing grounds to turn things on makes them easier to control with the car's computer. Pull fuse until it dries, then park in a more sheltered area.


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You must replace the ignition switch if you cannot get the key out.

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You cannot fix it, just replace it.

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Ignition switches have a pattern of spades on the back side that must match the replacement switch exactly otherwise you could end up blowing fuses or frying a coil. Hope this helps.

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