MTFCA Forum

last edit i think: Someone brought to my attention this being the wrong horn, I kinda thought so as well, I am not going to buy another horn any time soon, but what horn would be correct?

Edit again: Teflon on the bolt and a rubber washer before the nut fixed my issues.

Edit: how do I isolate the bracket from the steering column bolt, is there some sleeve to stop the bolt from touching the inside of said bracket?
I found that that was my issue.


I got a magneto horn for my 17 ages ago, and the bracket also ages ago but before I got the bracket I just sat the horn inside and ran the wires to it, it worked all fine. Today I actually decided to put it in right and I attached it to the bracket and the bracket to the car thus one went on the steering column bolts after doing all that it won't run on magneto. I need to get pics but what might cause this? Also I put a new wire from the button to the horn.

Since it's AC does it matter which wire goes to what post? Would that be it?

Also as much as I like to remove the horn to test, my firewall is wood and the square slot for one of the bolts is rotted a bit and I don't want to chance rounding that square more than it is

I have a hypothesis I think the Horn's body is grinding through the steering column Bolt because one of the bolts is off the steering column the other one just goes through the wood and isn't touching anything. Would grounding the outside of the horn kill the magneto power? Also how would I prevent grounding on that one Bolt just two rubber washers or is it more than that?

I switched the wires and now it will run off magneto but the horn won't stop sounding

With a little bit of multimeter probing it seems to me that the body of the magneto horn is shorting out through the one bolt on the steering column which is grounded and the body is indeed supposed to be isolated because one of the posts is directly on the body with continuity. Is there some sort of fail to rubber washer or something I need to put on?

I don't know if it helps or not but here's the picture of the back side of the horn it has one insulated and one uninsulated post

I would think both need to be insulated to the body. I think thats what you discovered in your testing/trouble shooting.

I just put a ton of Teflon tape around the threads then a rubber washer on that steering column bolt and it's all fine and dandy. Thanks though

The Top Right insulated terminal goes directly to the Magneto Post.

The Lower wire is providing a ground to make the horn blow.

The other end of that wire should go to the horn button.

The other wire from the horn button should go to ground.

Both of the horn wires should be black.

James has nailed it, I think. One wire to the magneto post. The second one goes to the switch. The top-of-the-column switch used on a 1917 model has an inbuilt ground connection in the form of a brass plate on the bottom that has a tab going to the other switch terminal.When the button is pressed, the ground is made and the horn blows.Relying on the column tube mounted to a wooden firewall is not going to work unless the steering shaft or the control rods make the ground.

On the Canadian cars with which I am familiar, the grounding device was deleted from the switch when battery horns were introduced and a second wire was added to make the circuit.

Allan from down under.

witch horn would be the earlier horn one with 2 posts or just 1 post I have both and was going to put one on my 1912 touring.

Colin, battery horns have just one post. I don't think I have seen a two post magneto horn, but that doesn't mean there is such a beast.

Allan from down under.

There's a photo above of a 2 post mag. horn !

Thanks Steve. Sometimes the "bleeding obvious" is not seen. I have no idea how such a thing would be wired up to work.

Allan from down under.

Allan wrote: ↑

Sat Jun 14, 2025 10:48 pm

Thanks Steve. Sometimes the "bleeding obvious" is not seen. I have no idea how such a thing would be wired up to work.

Allan from down under.

When a horn is attached to a wooden firewall it has no ground, hence the additional post for a ground connection.

The steering columns in early cars with magneto horns initially had a small tube to carry a single wire up to the switch on top of the column. That tube was fixed to the column with separate spot welded saddles. Then they devised a single wire U shaped tube. There was only a need for a single wire as the switch was used to ground the circuit via the steering column components. So, it looks like one wire from the mag post directly to the horn, and a second wire from the horn to the switch which is used to make the ground.

Two wires were run through a larger U shaped channel on the later cars with battery horns.

It looks like I was confused. Not that unusual when electrics are involved. The horns with one terminal are the battery horns. Being mounted on the engine an internal ground is assured. One of two wires up the column delivers power to the switch and the switch then delivers power to the horn, down the other.

Allan from down under, I think!