Wanted info on early 20 mag horn wiring

Discuss all things Model T related.
Forum rules
If you need help logging in, or have question about how something works, use the Support forum located here Support Forum
Complete set of Forum Rules Forum Rules

Topic author
Model T Mark
Posts: 235
Joined: Mon Jan 07, 2019 8:00 pm
First Name: Mark
Last Name: Eyre
* REQUIRED* Type and Year of Model Ts owned: 1913 Touring 1914 Touring and Roadster 1915 Touring 1926 Roadster
Location: Battle Creek Michigan

Wanted info on early 20 mag horn wiring

Post by Model T Mark » Thu Jun 24, 2021 11:06 am

The horn has two pole does the switch break the mag or ground? If the switch is wired hot here is the ground connected at the horn. If the switch breaks the ground where is that ground located. It’s a Canadian car with button in the middle of the steering wheel.

User avatar

DanTreace
Posts: 3296
Joined: Sun Jan 06, 2019 10:56 am
First Name: Dan
Last Name: Treace
* REQUIRED* Type and Year of Model Ts owned: '23 cutoff, '25 touring, '27 touring
Location: North Central FL
MTFCA Number: 4838
MTFCI Number: 115
Board Member Since: 2000
Contact:

Re: Wanted info on early 20 mag horn wiring

Post by DanTreace » Thu Jun 24, 2021 11:48 am

Normally the horn switch breaks the hot wire, but more info below.
canada.jpg
canada.jpg (14.53 KiB) Viewed 653 times
This info from earlier post:

By 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.

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.
The best way is always the simplest. The attics of the world are cluttered up with complicated failures. Henry Ford
Don’t find fault, find a remedy; anybody can complain. Henry Ford

Post Reply Previous topicNext topic