There are many reasons why a horn won’t work

Question:

Here’s a quick synopsis of my problem: I acquired this 1955 second series Chevrolet Pickup truck several years ago. As time allows, I’ve been focusing on specific areas that don’t allow for the ease of replacement/repro parts. The horns seem to be one of them. This truck has what I believe to be the original units, which don’t seem to respond to direct wiring and are fairly shabby looking.

I contacted a horn restoration specialist who said his cutoff was about 1957 and younger units for repairs, perhaps because of the lack of availability of internal components or lack of used units for cannibalization. In any case, it seems my choices of available fixes are plastic non-lookalikes or wandering through the aisles of eBay.

Horns can’t be that complicated and these two come apart easily so I’m prepared to take the in-shop restoration path if there’s some professional tutelage.

On the other hand I have no issue getting them to someone well-versed in their restoration.

It kind of depends on timeliness. I don’t want to wait for an extended period. The years slip away too quickly.

Answer:

Your truck, like nearly all vehicles of the era, came with an electro-magnetic diaphragm type horn. In simplest terms, there is a spring steel diaphragm with a “ringer disc” mounted in the middle of the horn housing. There’s an electromagnet comprised of an iron core wrapped with copper wire. When the horn button is depressed electricity flows through the wire winding and induces a magnetic field in the iron core. The magnetism pulls the steel diaphragm to the iron core, causing the ringer disc to strike the iron core and generate a vibration in the diaphragm that is audible. After the diaphragm moves a certain amount a small tab on it causes a set of contact points to open up, which in turn opens the electric circuit and eliminates the magnetic field. As soon as the magnetic field dies the steel diaphragm moves away from the iron core. When the diaphragm moves back to its rest position the points close and electricity again flows to the winding around the iron core, causing the electromagnet to again move the diaphragm. This cycle repeats itself many times per second as long as the horn button is depressed and electricity is flowing. The repeated vibration of the ringer disc and diaphragm is what generates the sound the horn makes.

So, with that background information about the fundamentals of your horn’s function, you can better understand all that can go wrong. The most common problem is severe rust that leads to holes in the diaphragm. Once the diaphragm has holes or is weakened by corrosion to the point that it loses its spring, the horn will stop making noise. If the contact points are corroded or broken the horn won’t work. If there’s a break in the wiring that prevents the electromagnet from functioning the horn won’t work. If the points are too far out of adjustment the horn won’t blow. You can take your horns apart and see what the sad story is. You may be able to fix the problem yourself, depending on what it is and how inventive you are. As you’ve already discovered, the internal parts for your horns are difficult to come by, which is why most professional restorers deal only with slightly newer ones.