6 to 12 V horn conversion

R

Russ B

Well-known member
How to Restore Your Model A, Volume 8, pp.110-112, has a reprint of an article by Bob Hess on "Converting to 12 Volts." Part of the discussion is about modifications needed so one can reliably use their existing 6 volt horn. I would recommend that anyone planning a 6 to 12 volt conversion should look at this article.

As the reprint is from a 1991 original article, revised 2002, I found one additional update that is still needed.

Because of the heavy current draw of a horn, the author indicates a small resistor, sometimes used for dropping the voltage, does not work when converting a 6V horn for use with higher voltage. He recommended an Ohmite Divideohm part 210-100-1 RO. That part number no longer is current. Since it took a bit of searching to find the current part number and a source where I could buy it, I am posting the updated number for anyone who can use it.

The new Ohmite part number is D100K1ROE.
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I found it at www.galco.com
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the other side shows how it is adjusted, moving the slider bar in the middle:
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The author also recommended adding a relay to the horn circuit as a means of getting a stronger current to the horn. I built a small test circuit, shown below, to be able to test and adjust the sound of my horn.
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My horn still needs some adjusting as I put it together from several different, older (mostly aftermarket) horns and replacement parts. The little 2X3 board is just a simple mounting arrangement of the components of the circuit. Once I get it all adjusted, I will permanently mount the relay and resistor on the floor pan under the seat.
 
Given that the horn is seldom used and even then in VERY short bursts, the in-line resistor that the vendors sell works just fine. While your solution is just fine, it is gross over-kill IMHO.
 
I haven't tried it yet, but I have always wanted to try two horns connected in series on a 12V system. It would have one horn under each headlight. I feel it would be a good noise.
 
Since converting to 12 volts removes the car from the realm of original, why not use a new 12 volt horn from A&L and sell the original to someone who is restoring an original car?
 
One other thought, since most people that are converting from 6 volts to 12 volts find themselves purchasing a different ignition coil that is compatible with the 12 volt system, that leaves them with a 6 volt coil that is no longer used. Why not use the 6 volt coil as the resister??
 
Bratton's sells a small resistor that you place inside the horn cover.. very small works great.. I have been using one for approx 10 years. 5 min installation
 
Adding a resistor to a 6V motor for 12V operation is not a conversion. It is a dirty fix that converts an amount of energy equal to the motor draw into heat. A true conversion would involve rewinding the field coils so no resistor is needed. The armature remains unchanged. After this is done you will need only half the amperage a 6V+resistor setup will draw. No relay will be needed. No need to put a resistor that will get smokin' hot during a parade under a flammable seat. There have been several write-ups on how to do this.
 
dave in australia said:
I haven't tried it yet, but I have always wanted to try two horns connected in series on a 12V system. It would have one horn under each headlight. I feel it would be a good noise.
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Interesting........stereo ahooga's would certainly sound better than the jerks always driving by the house with there 500 watt stereos shaking the windows.:mad:
 
Tom Wesenberg said:
Interesting........stereo ahooga's would certainly sound better than the jerks always driving by the house with there 500 watt stereos shaking the windows.:mad:
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There are black boxes to clone/hijack blue-tooth links. With a 5 Watt transmitter and a digitized horn mp3 file you could override and make their bluetooth enabled 500 watts go AHOOGA! as they drive by. LINK1. . .LINK 2
 
2manycars said:
Since converting to 12 volts removes the car from the realm of original, why not use a new 12 volt horn from A&L and sell the original to someone who is restoring an original car?
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This has got to be in the running for the "Top Ten Silliest Comments by a PURIST" awards.

Here's a link to a pdf version of a post I made to the old FordBarn about converting a horn to 12v.

I got my wire from McMaster-Carr. Radio Shack no longer carries a suitable wire for this project.

http://originalmodelaparts.com/Misc/WayHornRewind.pdf

Joe
 
We have had good luck soldering a shunt wire across the two wires comming out of one of the feilds in the horn. This basically puts that feild out of service, allowing the horn's rpm level to stay the same other than double. Did mine quite some time ago still works fine.
 
JoeWay said:
This has got to be in the running for the "Top Ten Silliest Comments by a PURIST" awards.

Here's a link to a pdf version of a post I made to the old FordBarn about converting a horn to 12v.

I got my wire from McMaster-Carr. Radio Shack no longer carries a suitable wire for this project.

http://originalmodelaparts.com/Misc/WayHornRewind.pdf

Joe
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I did not think it was silly, I thought it was a good alternative. I have had friends who did just that. I dont consider myself a purist, either.
 
I also use the old repro ahooga horns. most will work just as well on 12 volt and are much louder.The one on my roadster is marked 12v. I didn't like the sick cow sound of the old original horns. You could smell the smoke even on 6 volt. I also figured if I needed to use the horn as a warning, nobody would hear it. My horn is good and loud, we like it and it looks pretty close to like an original after installing a name plate. I also have an original on the shelf that works if anyone needs one, it came off a november 28 leather back fordor.
 
I rewound mine. only took a couple of hours. The starting current of the motor is higher than the running current, with the dropping resistor, the motor slowly gets up to speed. If you use a lower resistance, the motor starts fine and then runs too fast. Not really a problem unless you do a lot of parades, where the horn is run semi-continuously.
I don't remember for sure but I think I removed 50 turns of 20 gauge wire on each field and replaced them with 100 turns of 24 gauge wire. Now it runs just like it did originally on 6 volts.
 
Purdy Swoft said:
I also use the old repro ahooga horns. most will work just as well on 12 volt and are much louder.The one on my roadster is marked 12v. I didn't like the sick cow sound of the old original horns. You could smell the smoke even on 6 volt. I also figured if I needed to use the horn as a warning, nobody would hear it. My horn is good and loud, we like it and it looks pretty close to like an original after installing a name plate. I also have an original on the shelf that works if anyone needs one, it came off a november 28 leather back fordor.
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I have three of these Western Auto horns hanging around. One came with the truck, one I picked up at a flea market and the last I bought because it was marked 12v.

Using them on 6V definitely they're different sounding. The 12V used on 6V gets the sick cow award. But I've also noticed that the horn underneath the covers are the same, but that the field winding is parallel on one (6V) and series on the other (12V)

So maybe it's possible to examine one's original or other horn and make a change in the field wiring and do away with resistors?

Maybe one of the horn rebuilders could comment? We're a pretty knowledgible crowd around here.

Joe K
 
The original horn feeds the power through one field winding, then through the armature, and then through the other field winding, so it is a series winding already.
 
Tom Wesenberg said:
The original horn feeds the power through one field winding, then through the armature, and then through the other field winding, so it is a series winding already.
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So this would make sense that an original spartan horn COULD NOT be made into a 12v machine without rewinding/resizing the field coils. Thus the need for a voltage reducing method such as the rheostat.

Thanks for that.

My current horn of choice is one of the more recent "no-name" horns which emulate the Sparton including the taper of the tube and the curve of the trumpet, but is not marked sparton nor sold as one of the aftermarket spartans.

Well, I do look for "buys" on Ebay. Given a sparton tag it may appear to be the right horn to the casual observer.

Close enuf for now.

Joe K
 
Joe K said:
I have three of these Western Auto horns hanging around. One came with the truck, one I picked up at a flea market and the last I bought because it was marked 12v.

Using them on 6V definitely they're different sounding. The 12V used on 6V gets the sick cow award. But I've also noticed that the horn underneath the covers are the same, but that the field winding is parallel on one (6V) and series on the other (12V)

So maybe it's possible to examine one's original or other horn and make a change in the field wiring and do away with resistors?

Maybe one of the horn rebuilders could comment? We're a pretty knowledgible crowd around here.

Joe K
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My first horn came from J.C. Whitney in the seventies It still works good on 6v All of my repro horns adjust through the bell. I think some are Hutchins they all have one screw that holds the motor cover. One of the 12v horns has a slightly longer rear cover and is pretty loud.
 
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