Not much thought is given to car horns—unless they don’t work or they sound like someone with a bad larynx.
Aside from the obvious safety concerns, car horns are also about sound—and harmony.
Do they get respect when you bump the button? Most vehicles have two horns, a high and low pitch to create a harmony and a sound that can be heard. Some older vehicles have one horn, which doesn’t get any respect.
How a Typical Electric Automotive Horn Works
Few of us understand how car horns work. They are not an air horn, like a train, semi-truck, or a fire engine. They consist of a vibrating spring steel diaphragm that cycles several hundred times a second through a die-cast megaphone horn body that trumpets the high or low pitch sound. Those who understand music have often called this combination A and C harmony—the ordinary every day horn harmony heard everywhere.
The challenging part of horn function is how to get the spring steel diaphragm to vibrate with consistency. It has to work smoothly every time. Inside the horn’s seashell-shaped body, there’s an electromagnet, contact points, and a diaphragm. While at rest, the contact points are closed, which carries electricity to the electromagnet when you hit the horn button. When you press the horn button, this activates the copper coil electromagnet, which oil cans (oscillates and vibrates) the diaphragm. This turn of events opens the contact points, de-energizing the electromagnet and relaxing the diaphragm.
When the diaphragm and electromagnet rest, contact points close, energizing the electromagnet again. This hyper action happens hundreds of times a second, causing the diaphragm to oscillate rapidly, which makes a buzzing sound we hear as the horn’s bellow. This oscillation blasts through the coiled die-cast megaphone housing, which trumpets that loud 95 decibel sound from the horn’s bell mouth.
Why Do Car Horns Stop Working?
Car horns fail for three basic reasons: contact point damage or corrosion, electromagnet coil burnout, or mechanical seizure due to corrosion. Road dust and rain get into horns and cannot escape, which causes corrosion—a horn’s greatest enemy. Deterioration abounds.
Vintage car horns require a lot of power (about eight or nine amps) and operate at high frequency. The only electrical components in your car that demand more electrical current are the starter and headlights.
Horns survive for a long time because they aren’t used often enough to wear out. Yet, they also suffer from the lack of use, which causes deterioration.
How to Fix, Repair & Restore Your Vintage Car Horn
We’d like to show you how to fix your car horns, however, they are not always a component you should service yourself because they require extensive technical know-how. That’s when you need to seek the expertise of a vintage car horn rebuilder. Several of them can be found on the web.
At the moment, parts are not available for the larger behemoth pre-1965 car horns like you hear in old sitcoms, which are easier to service because they have a removable cover for easy access to the electromagnet and contact points. They trumpet a triumphant harmony. The bad news is parts are not available for these older horns, which means you need to find good cores.
Another important consideration with the larger earlier horns is the horn relay, which was used only with these larger trumpeters. When these horns stop operating, check the relay first with a test light or multimeter to make sure power is getting to the horns. Keep in mind, car horns do not tolerate electrical weaknesses. They must have 12 to 14 volts and solid connections to positive power and to ground or they will not function properly.
Jim Smart is a veteran automotive journalist, technical editor, and historian with hundreds of how-to and feature articles to his credit. Jim's also an enthusiast, and has owned and restored many classic vehicles, including an impressive mix of vintage Ford Mustangs.