You've probably heard it before -- a horn that won't stop blowing on some unfortunate motorist's car. It's not a common problem, but it does happen. And if it happens to you, it can be embarrassing and annoying -- not to mention loud.

If you know what to do, you can stop a stuck horn from blowing. Here's what you need to know:

When a horn won't stop blowing, the problem is usually caused by one of three things: the horn-ring switch in the steering wheel has remained closed, the horn relay has remained closed, or the horn wire that runs up the steering column has a break in the insulation and is touching bare metal. Probably the more common causes are the relay or horn-ring switch.

The easiest way to stop a horn from blowing is to simply disconnect the horn wire. A wire attaches to the horn (the "hot" wire), and the ground (which, basically, allows a complete electrical circuit) is where the horn bolts to the metal body of the automobile.

Pulling the horn wire from its connector is easy. Simply locate the horn (or horns, as the case may be), and pull the wire from its connector. Some cars have one horn -- in which case you'll have to disconnect only one wire. Many cars have two horns. In this case you'll have to disconnect the wire from each horn.

Sometimes, though, it's difficult to reach the horn because of its location. The horn is generally at the front of the car in the grill area, but it may defy a clean shot with your hand at the connecting wire. In any case, be sure the engine is off when you are searching for the horn -- you don't want to get your fingers caught in any moving parts. Also be sure you don't have any jewelry on your fingers or wrists. And don't wear any clothing that might get snagged on a bolt or other protrusion.

If the horn is not easily accessible, another way to silence it while you collect your wits is to disconnect the negative battery cable. This eliminates the electrical source your horn is using for power.

Of course, that means that you'll need a wrench to loosen and remove the battery cables (or pliers, with the spring-type battery-terminal connector). If you carry an adjustable wrench, pliers, and a couple of screwdrivers as part of a small emergency tool kit, you'll have no problem. If not, then you'll have to borrow a wrench or pliers.

The negative battery cable is marked, often with a minus sign or with an abbreviation, such as NEG.

After you have removed the negative battery cable, you can carefully work your hand into the area where the horn is and disconnect the horn wire. After the horn wire is disconnected, replace the negative battery cable and take the car to a garage.

One difficulty with something like this is that it's not the easiest problem in the world to trouble-shoot. Sometimes a sticking relay will come unstuck when its electrical power supply is cut off, as it is when you disconnect the battery cable. And after the power is turned on again, the horn may work normally for a while.

If the problem is caused by a bare wire that only occasionally rubs against metal, this, too can be hard to trouble-shoot. The easiest problem to trouble-shoot is when the horn starts blowing as soon as the horn wire is reconnected. In this case the mechanic can find the problem quickly. A horn that sticks intermittently, though, can be a tough nut for the mechanic to crack.