The horn is actuated by an electrical current. When the horn button is depressed, the relay carries light current to the relay which closes the connection. Most horns require heavy current in order to get the horn to work. But to have heavy current going through the relay to the steering column is very dangerous business. The relay keeps the two currents separated. If the relay is faulty, the horn will not work because the current will not shut the switch. Depending upon the part of the system that has malfunctioned, there may be parts that have burned out due to the high amount of current needed for the horn. On the other hand, a malfunctioning relay may cause the switch to shut and the horn to turn on even when the button has not been depressed by the driver. The horn relay is very easily replaced when it goes bad. It is located in the fuse box in most cases.