Last year I found, what I think is, a magneto horn on a swap meet here in Belgium. It was cheap and dirty and I brought it home for €7.-.
Now I am trying to make it sound as a horn but sometimes it make noise on the magneto of one of the T's sometimes I can't get it buzzing.
Can someone walk me through this repair. I cleaned it out and measured the resistant of the coil 1.2 ohm and from coil to body it is open.
Connecting to the car, should one terminal go to the magneto and the other to the horn button to the ground?
Can I find somewhere a new diaphragm? this one is rusted ?
I can't help you with troubleshooting, but you are correct about the wiring arrangement. One terminal is wired straight from the magneto. The other goes to the horn button, which completes the circuit to ground when pressed.
If you can get an old ac model train controller (transformer with a speed control), its a good way to test the horn. Mine came from a Marx Train set. Don't know if they were in Europe. Lionel would work also.
Try Moonshine County Antique Auto Horns in North Carolina here in the States.
The owner is Larry Rose. If you send him a pic of the horn and parts he may can tell you if he replace the diaphragm.
He repaired my battery horn on my 21 Touring.
Also try Langs. They may know of someone who repairs magneto horns. Another source is Fun projects. The owner makes diaphragms for battery horns.
Adam Doleshal at firstname.lastname@example.org repaired mine. Now I use it more often than the hand Klaxon.
You can operate the horn with a HCCT (it puts out an AC Voltage).
The coil in the horn is not grounded to the case. This is why there are two terminal posts on the horn.
One must be grounded when installed on the car.
The battery horn diaphragm that I make is fabricated from Stainless Spring Steel and it can replace the diaphragm in either the battery horn or magneto horn but the trick is drilling the center hole in it just right since you need to transfer the adjuster from the diaphragm you have to the center of the new one. That is not too difficult if you have a lathe. The adjuster is swaged to the center of the diaphragm. For my son's mag horn I made a new adjuster out of soft steel after robbing the center threaded part out of the old adjuster. They are often a weird thread but you might be able to rethread it to a new modern thread since it only has to be adjusted once.
Use a dial caliper and measure the exact OD of your diaphragm in a couple of places and I can size you up with a diaphragm and will drill you a center hole in it that you can then ream out larger as you need it. Stainless is not easy to work with but my son's repaired horn has honked for a long time now.
John I will contact you about this.
I take up this tread because it is finally done.
To complete the rebuild I needed a few little hand to help.
Here is what we have done.
I ordered a new diaphragm at fun projects. John machined the diaphragm what was needed to fit the magneto horn.
I punched the center part in it and cleaned up the tread.
For the coils I found that one side was connected to the housing and the other terminal should be insulated and connected to the switch and the magneto. The insulation was missing for a great part and needed to be rebuild. I used there for two coil box insulating washers and 2mm plastic hose that fit just over the new screw.
As all was back together I used my HCCT to test the horn and after a few adjustments of the center mushroom it buzz again. Should it be reset on the magneto of a running engine?
In the attachment a few photos
Amazing what can be done on a dining room table.
(And my garage is a mess).
Thanks for the explanation and the photos - especially the two "soon -to -be mechanics".
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.
On Andre's horn I 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.
Nice job Andre - Cute kids too. Glad your project all worked out since I wondered if it all went OK.
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.
It took a while to finish the horn but it will be on the woody next weekend.
After reading your explanation about the 2 amps setting I went back to my HCCT and tried to set the horn on 2 amps, I became louder. I think on the car it will sound just awful.
Thanks again for the help and advises.
I have adjusted the one on my wife's '18 Touring for max volume, but it is still not very loud. Are there any modifications that can be done to make it louder? Should it be disassembled and cleaned/inspected? What would cause one to not be very loud?
Hal, now you know why Ford added the louvers in the hood with the 1916 magneto horns.