Another Horn Question

Gufshoz

Gufshoz

Member
Hey everyone. I have an issue with a Spartan horn that was given to me by a friend. It works perfectly on my bench using the current 2 horn wires, but when I ground it to my A by mounting or just touching the car, it won't work. I'm currently using an old beeping horn that is not connected to the horn rod, but has a separate button. When I use that button and don't ground the Spartan to the car, it works. I'm looking for some sort of short in the Spartan, but can't find it. A continuity tester shows connection from either horn lead wire to the horn body or to both lead wires. The insulating base for where the two leads are connected is intact. I know that I'm missing something that is probably simple, but I am simple.
Thanks
 
There are two insulating washers each side of the brush holders, where they screw to the frame , check they are there, Or your horn button wire at the top or in the light switch is not completing the earth,
 
" A continuity tester shows connection from either horn lead wire to the horn body or to both lead wires."

There should be no continuity from the horn lead wires to the horn body. Check the washers that quickchange talked about or look for another path from the lead wires to the horn body.
 
Slip a piece of paper under the brushes and check to ground again, then check a commutator bar to ground, then the circuit will be divided 3 ways and you should be able to figure better where the short is
 
Kurt in NJ said:
Slip a piece of paper under the brushes and check to ground again, then check a commutator bar to ground, then the circuit will be divided 3 ways and you should be able to figure better where the short is
Click to expand...

Nice.

One can see the horn circuit at the classic Model A wiring diagram.

https://lesmodela.files.wordpress.com/2017/10/wiring-diagram.pdf

One should note that the switch which controls the horn is on the "downstream" side of the horn: the horn is "live" and you sound the horn by completing the circuit (effectively "grounding" the horn and providing a path of current to ground.)

The symptoms you describe are those of a grounded but not open circuit horn. The "paperwork" will tell you where to find the interior short.

I might hazard a guess and say the "ground" is "upstream" of the horn: examine the wire first which connects to the terminal block (i.e. "yellow wire.") - follow it into the casing and around inside. If it were the "downstream wire" (blue/yellow) your horn might sound all by itself without pressing the button.

Or (worse) it could be the armature. Isolating (paperwork) will allow you to check the commutator "bar by bar" and find the one coil which is shorted to the armature core.

There are those who offer "reconditioned" armatures. Sometimes reconditioning can be as simple as a coating of "Glyptol" insulating paint on the exposed copper wires connecting core to the commutator.

Joe K
 
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Thanks for the replies. I'm probably missing something basic. I believe that my horn is being grounded by the headlight bolt rather than the horn button completing the circuit. By using the paper to isolate the brushes, each wire has continuity through the field coils to the brushes. Keeping the brushes isolated, everything else is on one circuit: commutator, armature, windings, shaft, field poles and the horn body. Since one end of the shaft rides on the adjusting bar, I don't understand how to isolate the inner circuit.
Gufshoz
 
You have a short somewhere in the horn assembly. With brushes isolated from ground (motor frame). The field coils should been open with respect to the horn frame.
 
If your horn sounds when connected to the battery then it is functional. If there is power from the connection between the generator and the horn then there is only one thing left. The light switch/horn rod has a wire inside that can deteriorate to an open condition. There are kits to install a new wire. The kit includes a new contact for the tip of the rod where it contacts the light switch contactor plate that in turn is connected as the ground side to the horn. The horn motor is a shunt wound motor so it is not polarity sensitive. Connect it any way that fits well on the terminal plate inside the horn cover.

There is also a thin copper split bushing that fits into the steering shaft at the top where the rod slides in. That copper bushing helps pass the ground path through the steering shaft and on through the frame's ground plane. All this stuff has to make good contact for the horn to function as it should.
 
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