Horn wiring question

[purplewg]

I did search here but haven't found my issue so I am looking for help. Again I am working on my buddies 30 Model A. He said the horn wasn't working. I did some checking and got down to the horn itself. When I took it apart I found someone had been there before me and one wire was broken at the terminal on the inside coming from the motor. I soldered new wires on, cleaned and oiled. Thought that would do it. When I went to mount the horn back on the car the mounting bolt sparked. I took it back apart and made sure neither wire was grounded to the frame of the horn. I then just took motor and hooked it to the hot wire coming from the generator and grounded the other side with an jumper. It ran just fine. I put it back together and tested like this one more time and it worked. When mounting it, it sparked again. I built some insulators to isolate the mounting screws and it works just fine with the button. What am I doing wrong? When I took the horn off the mounts were all rusty and just fell apart. Are there supposed to be insulators between the horn and the mount? Thanks in advance.

[tinkirk]

Not that I know of
Anyway mine don't


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[Bob from Northport]

No insulators. You would loose the ground

[Tom Endy]

The motor section of the horn is isolated from ground. You can apply ground to one terminal and power to the other and the horn will work. You can reverse the leads and it will still work. I suspect you have the horn section grounded somewhere.

Tom Endy

[nkaminar]

Is the screw too long? It could short out the horn if too long.

[Ruth]

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Originally Posted by Bob from Northport

No insulators. You would loose the ground

Model A horn does not need to be grounded. it is grounded thru the horn button.

[purplewg]

Thanks for the replies. I guess I will have to pull it off and start checking again with the DVM. I checked to make sure there was no connection between the two wires and the case. Makes me wonder if the screw that holds the motor case on the back needs an insulator. It screws right through the case and into the motor housing.

[bobbader]

You mentioned you thought "someone was in there before me" (excuse my paraphrasing). If so, and depending on how far they might have gone, there are key insulators they might have missed. Specifically, there are fiber insulator washers under the flat head 10/32 screws that attach the brush holders to the motor frame and as well on the inside of the frame under said brush holders. These are often left out or ruined in reassembly of motor parts and cause a direct ground to these parts that are otherwise electrified. The inside fiber washers are flat while the ones under the screws are conical to conform to the taper under the screw head.

Also in the mix (but I don't think prevalent here) is that some horn cover screws may have been replaced over the years with plain hardware store replacements. The original screws had an enlarged shoulder above the threads providing a "stop". This stop would allow the screw to be fastened just enough to hold the cover in place without contacting any electrical components. A longer screw or a screw with threads all the way up to the head can be screwed in far enough such that it touches the brush holder, causing the same ground as outlined above.

Hope this helps. Good luck. Bob Bader

[Bob C]

As mentioned the cover screw can be to long and contact the brush holder.

[purplewg]

Originally Posted by bobbader

Also in the mix (but I don't think prevalent here) is that some horn cover screws may have been replaced over the years with plain hardware store replacements. The original screws had an enlarged shoulder above the threads providing a "stop". This stop would allow the screw to be fastened just enough to hold the cover in place without contacting any electrical components. A longer screw or a screw with threads all the way up to the head can be screwed in far enough such that it touches the brush holder, causing the same ground as outlined above.

Hope this helps. Good luck. Bob Bader

Thanks Bob, I thought I replied to this yesterday but I don't see my response. lol I think you maybe correct on that screw. I remember thinking it did not look original. I am going to check it out today.

[purplewg]

Originally Posted by Bob C

As mentioned the cover screw can be to long and contact the brush holder.

Thanks Bob, I will check it out. I also watched a video the other day where the guy discovered the diaphragm was in backwards on his. Mine was the same way. lol

[purplewg]

Ok you guys are the best! It was the screw. Not original and too long. Works fine now. Thanks again

[bobbader]

Great ! Always nice to find out why something went wrong. In this case, it stopped any electrical disaster and your horn now works well. Good Going.

Bob