There is no mistaking the classic "Ah-Ooga!" sound that came from early car horns. Commonly known as the "ooga" or "klaxon" horn, this device is still popular among enthusiasts of antique cars. To get just the right sound from an ooga horn, you need to adjust the tension in the mechanism that controls the horn vibrations. While the specific methods of adjusting various models of ooga horns may differ, the basics remain the same.
Look for an adjusting screw on the back of the horn. Usually the screw will be conspicuously placed and easy to identify as an adjusting screw. Sometimes the screw will be marked "Adjust." On older horns, you may have to remove the back cover to find the adjusting screw. On many newer horns, you can find the adjusting screw under the front cover.
Check to see if the adjusting screw is held by locking screws. Many times one or two locking screws hold the adjusting screw in place. If so, you will have to loosen the locking screws before turning the adjusting screws.
Turn the adjusting screw until you get the right "ah-oogah" sound. It may take a little trial and error. When you turn the screw, you are changing the tension of the components that produce the sound vibrations. Make sure you tighten any locking screws when you are done.
Adjust the current to the horn to change the volume. Many horns have current adjusting screws inside the horn. The screws allow you to adjust the current by changing the size of the "air gap" between two electrical points. Turn the screw to the right for more volume or left for less. The location of the screw will vary from horn to horn, and some horns may not even have a current-adjusting screw.
Many older horns are designed to run off of 6 volts instead of the 12 volts supplied by modern batteries. This may cause your horn to be too loud, and over time the extra current can damage the horn. You can reduce the current and the volume by installing a dimmer switch on the wire going to the horn.