MTFCA Forum

Got a question, is the battery horn's diaphragm the same diameter as the magneto horn and can it be used as a replacement? I know this seems like a stupid question, but I need to ascribe a part number to the diaphragm and the only one I can come up with is the one for the battery horn.

On and one more thing....on the magneto horn, this picture shows the ground post as having a fiber washer a nut and a jam nut on this post....the other post is labeled "Horn Switch or Magpost for Testing"? Is this correct? I would seem to me that if you're going to have an insulated post it should go to the high voltage (magneto) side of things rather than the bloody ground. Since I really don't know much about these types of horn, I thought I'd ask you guys....I need to know so I can get the drawing correct (the first time, which would be a novel experience, lol).

The magneto horn diaphragm has an adjusting nut and boss in the centre. The battery horn is a pain disc. They may be be the same diameter, but I doubt they can be substituted and operate properly.

Allan from down under.

IIRC, the magneto horn should NOT have an insulated washer, as it is grounded through the bracket. The only wire coming to the horn is the hot wire coming from the button.

Keith, that's why I think this photo is mislabeled when it comes to which side is the hot side....made absolutely no sense that the ground wire would've been an insulated post. This not my photo, somebody sent it to me to show how the mag horn was supposed to be wired thanks for the correction.

Allen, yes there is a nut in the center of diaphragm on a magneto horn, but there is nothing stopping somebody from using the batteries horn diaphragm either if it is the same diameter, because it certainly must be the same thickness. All you'd need to do is scribe out where the center of the diaphragm is and drill a hole in it and then install that adjusting nut that is sold from the parts vendors and you're done....certainly has enough hole along the outside to accommodate just just about any horn with the same size diaphragm, probably would even fit a Model A's Sparton too, they're about the same size as I recall.

I can't seem to find my copies of wiring diagrams, but I am 90% certain the early magneto horns required both post to be insulated, as the horn was wired "hot" with the steering column mounted horn button providing the ground. The wire tube on the early units was a small tube that held one wire. Later on this tube was replaced by a "U" stamped metal piece that could hold two wires, and also for a time, the headlight wires too. The early horn button was fastened to the top of the steering tube with two screws, one of which clamped down on the ground connection brass strip from the button contacts.

KWTownsend wrote: ↑

Thu Sep 16, 2021 11:36 am

IIRC, the magneto horn should NOT have an insulated washer, as it is grounded through the bracket. The only wire coming to the horn is the hot wire coming from the button.

If the magneto horn only has one wire is the photo above wrong? Asking because I purchased a mag horn from a member on hear and should be at my home soon. I hope to install it in the next few days on my 1915 Touring.

Thanks
Ron

Ron, If your car has the column mounted button that is held on with two screws and is on a top side of the column, with only one wire going to the button, then YES, the photo is wrong! The horn button provides the ground circuit and the hot side comes from the magneto.

It is impossible to ground the horn through the bracket like somebody has said, because that bracket mounts to the firewall and the firewalls are all wood, were clear up through the middle of 22.

Now the single post magneto horn may be for the metal firewalls for those vehicles that were called the "Non-Electric", these vehicles were typically commercial, that's why I've got a drawing of the 26-27 switch with the ammeter

and without one.

These vehicles probably had the single pole like "Heco" brand horn (they have a sort of conical style back shell).

I don't know for sure, but it seems logical, since they are single pole which would indicate that ground is through the horns shell and the bracket or through the switch. The other photo shows one side of the leads soldered to a post and the other to the back itself.

I dont think this is correct: "It is impossible to ground the horn through the bracket like somebody has said, because that bracket mounts to the firewall and the firewalls are all wood, were clear up through the middle of 22."

Instead I think the correct answer is that the 1915 mag horn is clearly and directly bolted to the steering column where the horn button is screwed down, and the column housing grounds the horn system all together.

There are 2 screws affixing the horn bracket in the engine compartment to the car, and admittedly one of them is screwed into the wood (firewall), but just for additional stability, but not as a ground. The other affixing bolt grounds the horn to the steering column to which the steel horn button housing makes contact and is screwed down on. So that may be where the confusion comes in as to where the ground is located.

I have had a variety of 1915s over the many years, and the horn system on the about 10,000 brass bell mag horn cars they built is somewhat confusing, so some photos might help. There is just one horn wire out to the horn from the button. I think the brass bell mag horn cars were all built in Jan.1915, as I recall, but I can't quote you a source and I certainly could be wrong as I wasn't there. But that seems to be pretty consistent with the dates on the authentic mag horn cars or chassis I have seen. And it is fairly tough to find a real 1915 steering column. The wire tubes on the 1915 columns are designed differently a than the later year car horn tubes, so you really can't cheat and use the horn wire tube from a later column and put it on a 1915 column if you are a real authenticity bug, but I have actually done that to give the horn wire some protection going out to the horn. The 1915 tubes were really sort of experimental, and had more welds and parts tacking things together. Ford cleaned up the wiring covers in later year productions and made them with fewer parts, and the welds on the later ones were different from the 1915 horn tubes.

I will try to post some photos explaining this:

Some more 1915 horn set up photos

Some more 1915 horn button pics:

John Regan gave this explanation of the two versions of the magneto horns:

John F. Regan on Thursday, September 10, 2015 - 09:25 am:
Mag horns are wired 2 different ways. The early mag horns have both electrical connections isolated from the horn housing and thus isolated from ground. These are used on the 1915 to early 1917 or so. On those cars one connection of the mag horn is connected to the mag post of the motor and the other connection goes up the steering column to the horn button where it is grounded to complete the circuit and honk the horn. On late mag horns one of the connections is wired directly to ground internally and there is only a single outside power connection for the horn.

On the later cars a wire from the magneto goes up to the horn button and then the button completes the connection to another wire that goes down the column to the horn connection. Thus the horn button supplies a "hot" power connection to the horn. The mag horn housing MUST be grounded on these horns. During the transition years the magneto horns were supplied with 2 isolated connections but one of them had to be grounded when used on later cars. This grounding of one of the connections was accomplished by simply removing the outside hardware and insulation washer and then putting the hardware back in place without the insulating washer to thus ground the connection to the horn housing. The horn then had to be mounted with a good ground to its housing.

Thus you can make an early horn (with 2 connections) work on any T with a magneto and horn button but you cannot use the later magneto horn on the early T unless you go inside of it and remove the internal ground connection and then redrill the horn and bring out the previously grounded connection so that it can be grounded by the horn button as used on 15-early 17.

I have used a battery stainless steel diaphragm and drilled a center hole in it for him but also then mounted the center on a mandrel to be able to spin it and slightly reduce the O.D. too. The battery horn diaphragm is just a very small amount larger on the OD when used on an early mag horn but it fits just fine on some of the later ones and even the perimeter holes line up on the later mag horns if they are Ford design rather than one of the other makes. I have not researched the whole thing that much to know which is which other than to be able to explain the electrical differences of the early versus the late and the 2 versus 1 terminal mag horns.


Mag horns were set for maximum volume with 2 amps drain using a test generator. That is what the drawings say but no detail was given as to what the generator was exactly although I suspect it was an HCCT. Mostly they just make some sort of noise. Anything from a screech to a buzz and all sounds in between are "normal".

My line on mag horns is that if you find one that sounds just AWFUL it is probably NOS.

Allan, hmmm, interesting, I never could figure out where that damned bracket mounted....off the steering column would be a great place, although it looks like it makes getting to the wiring a bit more cumbersome though. I think I've already done the horn buttons though...hmmm, maybe I should link those drawings up to horn drawings, hmmm.....got to cogitate on it some.

Dan, thanks, John explained pretty good, myself I don't even have an electric horn on my car, I've got a hand klaxon, which doesn't care what voltage the car runs on and it much louder than those mag horns or the electric ones, plus it sounds like it means business, rather than that strangling a goose sound.

Hi Martynn,
Yes, I have a hand klaxon on my 15 too; they are definitely the way to go if it's noise you are after. The brass bell mag horn is pretty much all show and not much honk.
Rollie

Anybody know what the screw size is for those 6 screws that hold the bell to the coil cover?

And what is the size of the mag horn adjusting screw?

To my older relatives, all cameras were Kodaks and all tissues were Kleenex. Of course those are brand names (not generic) for some cameras and some tissues. Not all fig bars are Newtons, and not all mechanical horns are Klaxons. Mine is a Stewart.

Yet you posted pictures of a Heco magneto horn that you were going to paint for your 15. The nut in the center of the diaphragm is usually the same thread size as any of the other mag horns (I think), I was just wondering if the adjustment/noise maker screw thread was a 10-32 or a 12-32 (12-32 would be an odd ball size, the more common one is the 10-32. But since I don't have one of these horns, I can't go out and measure it.

I was hoping somebody would tell the size here so I wouldn't have to take my horn apart again to find out.