# THE Definitive Thread on Horn Repair



## MaxGlide (May 16, 2012)

*How To Fix Your Horn*

After trying to fix non working horns and not finding all the answers online in one place, or no answers, I think I have figured out most of the angles on how to get a horn working. Please add anything I haven't thought of.

Here are the steps I recommend.

1. Clean the horn of all rust. I like using Evapo-rust. That stuff is AMAZING and will not hurt the paint, contacts, wiring. Just submerge the whole thing so it gets to everything inside the horn.  Follow instructions and MAKE SURE, the unit is COMPLETELY DRY  after you rinse it off. Like the bottle says, you can prevent further rusting by applying clean Evapo-rub on after drying it and letting it dry on. I used a small art paint brush to get it in crannies as I did not want a film on any contact spots so as to have any chance of interfering with a connection.
Here is a pic of before and after cleaning with the stuff. I did not buff anything, just scrubbed lightly with a toothbrush and a week later no rust yet.













2.Make sure all contacts are clean and free. I take little bit of fine emery paper and lightly sand the battery contacts in the tray then fold it over and put it between the button end and the copper tab. Depress the horn button and drag the emery paper through it. This will clean the switch exactly where it contacts. Now you need to see which section is the problem.

3. Put batteries in and test horn. No sound? Bypass the button/tray by holding the negative part of a D cell to the screw on the back of the horn and run a wire from the positive terminal of the battery to the lone wire sticking out of the horn. While doing this you can screw the adjusting screw on the perimeter of the horn in or out until you get sound. More on this function of this screw later. 
Still no sound? If you have another working horn, hook up the good horn unit to the tray you just cleaned and test it. It's only one screw and one wire to move over. If the good horn works in the tray you just cleaned, then the problem lies in the horn.

4. Still no sound? If you have a voltmeter (or a friend with one like me!) you can have them test the continuity of the circuit. This will tell you if a wire has rusted through inside. 
5. Still no sound? Time to go inside the horn unit. GENTLY  pry back ALL the little tabs holding it in. You can only do this a few times before they break off (learned this from experience) Don't leave, say, two tabs and try to slide the diaphragm out/in from the side. You must be able to put the diaphragm straight back on.  If the evapo-rust did its job, the inside should be nice and clean. Rub emery cloth between the adjuster arm and the switch. 

To test if the electromagnet is working, put some small, metal object on the end of the electromagnet and push the horn button. If it sticks to the magnet, your horn is working to that point and all that's left is to adjust the pitch screw. If you don't get a magnetic pull, then you still have a problem before that point. (batteries dead, circuit still broken, wire broken, switch tripped.)

Before proceeding it is good to understand how the horn actually works.

Online description of an electromagnetic horn....
An electromagnetic horn uses an electromagnet to attract a steel diaphragm and turns that electromagnet on and off rhythmically so that the diaphragm vibrates. In fact, it uses the diaphragm's position to control the power to the electromagnet. Whenever the diaphragm is in its resting position or even farther from the electromagnet, a switch closes to deliver electric current to the electromagnet. The electromagnet then attracts the diaphragm's center. But when the diaphragm moves closer to the electromagnet, as the result of this attraction, the switch opens breaking the contact, turning off the magnet and the  and current stops flowing to the electromagnet. Because of this arrangement, the diaphragm moves in and out and turns the electromagnet off and on as it does. The diaphragm's tone is determined by the natural resonances of its surface.





So in layman's terms, when you push the horn button, the small disk in the middle of the diaphragm is drawn towards the electromagnet. When it gets far enough, the disk pushes on the switch, breaking the contact and turning off the magnet and disk pops back to neutral. The constant on and off/back and forth motion gives you the horn sound. So how far you turn the screw will determine how far the diaphragm travels before tripping the switch. The further it travels, the deeper the sound. Adjustment is crucial because....

If you screw it in too far, it pushes the arm too far and permanently breaks the contact point, resulting in no creation of magnetic force when button is depressed. 
If you don't screw it in far enough, you get a magnetic force but the contact is never broken as the diaphragm can't travel far enough to break  the circuit and allow the diaphragm to return to neutral.

6. Once you get the depth of the screw right, put the horn back together making sure that the small disk on the diaphragm is resting on or above the switch and not beside it. It can end up beside the switch if you slide the diaphragm in from the side. Put outside housing on and test horn before you crimp the tabs back into place in case you have to do more work inside. 

So there you go.....if you follow those steps you should be able to get the horn working. So far, regardless of condition, I have managed to get every horn working.

Please add any info I have omitted.


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## Blueschwinns (May 17, 2012)

*Horn Repair*

WOW! Thanks for the information. I have two old horns I am going to play with.


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## halfatruck (May 17, 2012)

Appreciate the information, I also have horns that need work.....now I have something to go on....
Thanks


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## SJ_BIKER (May 17, 2012)

*I got a near NOS Delta...not working...*

I have one near NOS delta horn unit.  I cleaned and cleaned...these tips should help...thanks


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## MaxGlide (May 18, 2012)

Unless the horn unit is so badly corroded that it has eaten away the insides it is either the continuity of the  circuit or the physical adjustment of the screw. If you can isolate whether it is the tray or the horn via troubleshooting, it will make it a lot less frustrating.

Maybe an abbreviated list might make it easier then one can go into detail if it still doesn't work.

1. Clean all parts and contacts.
2. Test horn by bypassing the button and going direct battery to horn contacts
3. Test tray by hooking up a good horn to it.
4. Open horn and test function of electromagnet with paper clip on magnet. If it sticks, it is the contact on switch or the setting of the screw that is the problem.

Let me know how it goes!


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## Ignaz Schwinn (Jun 11, 2012)

Nice job Wayne!  I looked this up after talking about it yesterday.  Thanks for posting.


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## Kevinkay (Dec 20, 2022)

YES!  just fixed my horn thanks to this post.  THANKS!!

Going to add what worked for me as my horn is a little different.
Mine is 1.5 volt - 2 D batteries in parallel (increases amps but not volts) from J.C Higgins 1961 Flightliner.
After I opened the cover I was getting the 1.5vots up the coil but it was never creating a magnet until I figured out that the diaphragm (the vibrating disk) needs to complete the electric flow to ground (red arrow)- it then creates magnet that pulls the switch down - breaks the ground and it keeps repeating.  I needed to clean the contact points of the center of the diaphragm and the outside edge it makes contact with (blue arrows).  Also mine has a uninsulated wire that needs to be kept off on contact with ground (green arrow).   I used a hook blade knife to open the tabs (some of them I had to hammer the tip in).   

wanna go fast - go alone
wanna go far - go together


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## catfish (Dec 20, 2022)

Great info


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## videoranger (Dec 20, 2022)

to make sure your D cell horn and lights never suffer from the dreaded acid leak corrosion use AA to D cell spacer and use non re-chargable AA lithium cells ( these last much longer than re-chargeable lithium ion cells and can sit inside device for a long time without loosing power )
https://www.amazon.com/dp/B00EAKP8S...p_abs&ref_=aa_maas&tag=maas&gclsrc=aw.ds&th=1


			aa to d cell converter - Google Search
		

they last a long time when not in use and provide good power.
Very nice horn service post! Thanks MaxGlide for taking time to provide the tutorial with top quality pictures.
also a test light or volt meter will substitute for using a known good horn for testing battery and push button in the horn circuit if you don't have another good horn handy.


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