Jim Smart
April 26, 2011

Car horns are important to your safety. They’re also the voice of your classic Mustang. Not many of us think about how they work or what’s wrong with them when they stop working because we deal with them so rarely.

Vintage Mustangs are equipped with two horns--one high-pitch and one low-pitch to create that familiar harmony. Function is quite simple--a vibrating spring steel diaphragm that cycles several hundred times a second through a die-cast megaphone that trumpets the high/low pitch harmony. Those familiar with music have called this combination A and C harmony, the common car horn tone. Editor Donald Farr, who is also a bass player, checked his ’66 GT hardtop with a tuner, which registered an F to F# low pitch and an A for the high.

The tricky part of horn function is how to get the spring steel diaphragm to vibrate with consistency. Inside, you’ll find an electromagnet, contact points, and the diaphragm. At rest, the contact points are closed, which energizes the electromagnet. Hit the horn button and you activate the electromagnet, which oil cans (oscillates) the diaphragm. This action opens the contact points, de-energizing the electromagnet and relaxing the diaphragm. When the diaphragm and electromagnet relax, 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 whaaaaa! This oscillation blasts through the coiled die-cast megaphone housing, which trumpets that loud 95-decibel roar from the horn’s bellmouth.

According to Gary Steinkellner of The Horn Works, horns quit for three basic reasons--contact point damage or corrosion, electromagnet coil burnout, or mechanical seizure due to corrosion. He adds that road dust and rain get into horns and cannot escape, which causes corrosion, a horn’s greatest enemy.

Interestingly, vintage car horns require a lot of power (8-9 amps) and operate at high frequency. The only electrical components that demand more 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 absence of use, which aggravates corrosion.

There’s mixed news about classic Mustang horns. Although our intent is to show you how they work, they really aren’t a component you should service yourself because they require technical know-how. The Horn Works has the knowledge to rebuild and restore ’65-up compact Autolite Mustang horns. The good news is a Horn Works restoration not only gets your horns back in operation, it also raises the decibel level from 95 to an attention-getting 110 decibels.

Unfortunately, at the moment they don’t service the larger ’64 Autolite horns, which are easier to work on because they have a removable cover for easy access to the electromagnet and contact points. This is where we look to Ray Sanchez of Mustangs Etc. for his expertise. He’s going to show you how to get ’64 horns back into operation.

Another important point of consideration with ’64 horns is the relay, which was used only for the ’64½’s generator charging system. When these horns stop operating, always check the relay first with a test light or multimeter to make sure power is getting to the horns. And remember, car horns are intolerant of anything short of 12-14 volts and a rock solid connection and ground. Weak connections will render your horns inoperative.

If your horns are unserviceable or missing altogether, reproduction horns are available from National Parts Depot. Note that the reproduction bodies are secured by screws, not rivets per original horns.

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