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Old 05-15-2021, 07:02 PM   #1
1965 Mustang
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Default Horn Help

I have a 6 volt 1929 model A with a Stewart Warner horn which appears to be original to 1929 as the motor and insides look pretty old fashioned. It works good but there seems to be a very slight short to ground somewhere that gradually discharges the car battery. But not enough to sound the horn when just sitting. Again when everything is hooked up and the horn button is pushed on the steering wheel the horn sounds loudly. (If I put a test light between the positive/ground cable and the positive terminal on the battery it lights when doing nothing and goes out when the horn wires are disconnected thus indicating a slight current draw) I used a ohm meter and found there is always continuity between both of the input wires on the little insulating block under the horn cover and the mounting bracket on the horn body. So I am guessing there is a slight short somewhere in the horn. Or maybe I am off base and the whole trouble is in the horn button and/ or wiring to the button on the steering wheel. Any thoughts?

For a long time I used some cork gasket material and tape to insulate the horn at the mounting stud under the left head light and everything worked fine. Thank you

Thank you.
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Old 05-15-2021, 07:34 PM   #2
Ayers1
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Default Re: Horn Help

I had trouble along the same lines with my 30. Figured out if I took the back cover off there was no issue. Finally realized that the cover screw was too long and when I tightened the cover it would go in and short out. That would be a place to start.
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Old 05-15-2021, 08:44 PM   #3
Herb Concord Ca
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Default Re: Horn Help

The horn motor should be isolated from ground. You can't measure between the two horn terminals with an ohmmeter, you will always get a reading, this is normal. Either horn terminal to ground should be an open circuit.
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Old 05-15-2021, 10:10 PM   #4
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Default Re: Horn Help

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Originally Posted by Ayers1 View Post
I had trouble along the same lines with my 30. Figured out if I took the back cover off there was no issue. Finally realized that the cover screw was too long and when I tightened the cover it would go in and short out. That would be a place to start.
This is the first thing Id check. S-W horns are extremely well made, eeliable, and usually trouble free if maintained (oiled regularly!)
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Old 05-16-2021, 08:51 AM   #5
midgetracer
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Default Re: Horn Help

Check the wire on the horn that comes from the steering column(blue wire) and see if you have any continuity to ground. If not, the problem is inside the horn.
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Old 05-16-2021, 08:29 PM   #6
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The horn sounds when the horn button is pushed, completing a circuit to ground. With the leads connected to the horn, both electrical contacts will read battery voltage when measured to ground with a volt meter. When disconnected from the horn, one lead will read battery voltage, the other will read 0 volts. Try disconnecting the latter and see if the problem goes away. If it does, the fault is somewhere between the horn and the grounding point used by the horn button. If not, the fault is in the horn, OR the hot lead is leaking current to ground. Hope this helps.
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Old 05-16-2021, 11:12 PM   #7
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Default Re: Horn Help

Thanks for everyone's input. I figured out the problem, one of the very stiff uninsulated wires going to one of the field coils on the horn motor was bent slightly and just barely touching one side of the horn frame. I bent it back about 1/4 inch and problem solved.
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Old 05-16-2021, 11:40 PM   #8
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Default Re: Horn Help

Not entirely on topic, but worth repeating. If you ever decide to take a Stewart Warner horn apart to clean and fix, beware that the nut that holds the warbler to the motor shaft is a REVERSE THREAD. Turning it too hard the wrong way can twist it right off. (Don't ask me how I know this).
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