Horn

Tom F OHIO

Tom F OHIO

Well-known member
When I touch the wires on the horn they spark and the horn blows. Do I need to replace the horn rod. Also is only one wire suppose to show 6 volt? Thanks....
 
Tom - the horn operates on an interrupted ground basis. Power is fed to the horn, through the horn, then to the light switch bundle. When you depress the horn button you complete the path from the light switch bundle to ground, and the horn blows. At rest (button not pressed) and both wires connected, both terminals on the horn will show 6v to ground. If you remove the two wires from the horn one will show 6v to ground (and will spark if you touch metal), the other will show 0v to ground. On the one showing 0v, you will show open circuit (infinite resistance on an ohmmeter) to ground without pressing the horn button, and closed circuit (zero resistance) with the button pushed. Unless the button is pushed, they will not spark against each other because there is no path to ground.

Not sure what you mean by “when I touch the wires…”. The terminals on the horn are insulated from the metal housing. If you get a spark from pressing on the terminals you may be shorting to the horn case. You may need to rebuild that terminal block on the horn and be sure you have good insulation.
 
JayJay said:
Tom - the horn operates on an interrupted ground basis. Power is fed to the horn, through the horn, then to the light switch bundle. When you depress the horn button you complete the path from the light switch bundle to ground, and the horn blows. At rest (button not pressed) and both wires connected, both terminals on the horn will show 6v to ground. If you remove the two wires from the horn one will show 6v to ground (and will spark if you touch metal), the other will show 0v to ground. On the one showing 0v, you will show open circuit (infinite resistance on an ohmmeter) to ground without pressing the horn button, and closed circuit (zero resistance) with the button pushed. Unless the button is pushed, they will not spark against each other because there is no path to ground.

Not sure what you mean by “when I touch the wires…”. The terminals on the horn are insulated from the metal housing. If you get a spark from pressing on the terminals you may be shorting to the horn case. You may need to rebuild that terminal block on the horn and be sure you have good insulation.
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That is one place there could be an issue. So is failed insulation in the field windings or armature. To determine where the problem is, you will need to dismantle the horn is do some tests. That's all assuming the problem is in the horn.
 
Synchro909 said:
That is one place there could be an issue. So is failed insulation in the field windings or armature. To determine where the problem is, you will need to dismantle the horn is do some tests. That's all assuming the problem is in the horn.
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Thanks, Synchro, good points. I made the presumption that since he can get the horn to work the issue was likely external, not internal. At least that’s easier to troubleshoot.
 
JayJay said:
Thanks, Synchro, good points. I made the presumption that since he can get the horn to work the issue was likely external, not internal. At least that’s easier to troubleshoot.
Click to expand...

It might be my turn to modify what I said. If the fields or armature are shorting to earth, I don't think the horn would work no matter what he did. Hmmm.
 
When I hook one wire on the terminal nothing happens but then when I put the second wire on the terminal the horn constantly blows. Would that be in the horn button and if so is there any fix besides replacing horn rod.
 
There is a kit available from model A sources to repair for deteriorated horn rod internals. A volt/Ohm meter is the best way to test the horn rod assembly.
 
Tom F OHIO said:
When I hook one wire on the terminal nothing happens but then when I put the second wire on the terminal the horn constantly blows. Would that be in the horn button and if so is there any fix besides replacing horn rod.
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This explains it much better. Here’s how I would proceed:

1. Disconnect battery
2. Remove both wires from the horn and secure them so they don’t touch each other, nor any metal.
3. Reconnect battery
4. Using a voltmeter, determine which of the two wires is hot (6v to ground)
5. Take the other wire (the one NOT 6v to ground) and using an ohmmeter, measure resistance to ground. (I usually use the mounting bolt of the return gooseneck as ground, as it should be unpainted metal).
5A. If the resistance to ground is infinite (open circuit) then depress the horn button. It should go zero resistance or close to it (closed circuit). This is normal. If this checks out then your short to ground is not in the horn button.
5B. If the resistance to ground is zero or close to it (closed circuit) you have a short to ground somewhere. It may be in the horn button or may be in the wiring between the horn and the light switch. If you pull the horn rod by removing the clip and spring at the bottom you can test the horn rod separately. Rebuild it if necessary with the internals kit available from the vendors. Be sure to check the insulator at the bottom of the horn rod, where the internal wire is soldered on.

It’s best to do some diagnosis rather than just throwing parts at a problem.
 
Tom F OHIO said:
I have a good meter but not sure on how to test it. Does the button part come out somehow?
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To get to the button you need to pull the horn rod out. The button assembly is attached within the light handle by a keeper with four tabs, accessible from the back of the handle.
 
On a related note, I’ve found that it is very difficult to get the horn rod out of the steering column on the closed cars without removing the steering column and steering box from the car. You do NOT want to bend the horn rod, which is quite easy to do.
 
On a closed car, remove the bolts holding the steering column to the frame and to the gas tank and tilt the steering column down.

If the wire to the horn button is grounded, as described above, and you do not want to fix it by removing the horn button rod, you can run a temporary wire to a push button inside the cab somewhere that you can press to blow the horn. Run the other side of the push button to a good ground connection. You can epoxy a strong magnet to the back side of the push button so that you can mount it anywhere without drilling any holes. The push buttons for door bells work great. Some are lighted so that you can see the button at night. Place a piece of material behind the magnet so that it does not scratch the paint.

The complete electrical system is shown here, along with lots of information on all things electrical for the Model A: https://www.mafca.com/downloads/Seminars/2018%20Reno%20Electrical%20System%20Alex%20Janke.pdf
 
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