Horn resister

B

brokenspoke

Senior Member
My 1929 RPU is a 12 volt negative ground. I bought a Horn Resister (6 to 12 volt) from a supplier, the instructions show that its wired inline to the ground wire in steering column. My question does it matter where the resister is spliced in the wiring Neg or Pos ? (Spartan horn)
 
Horns are always hot all the time, then get activated when you ground the button on the steering wheel. Pos or neg ground, 6 or twelve volt , all the same. So, if the manufacture wants it in the ground side to the button, thats what I would do. My favorite 12 volt horns were the mid twenty's dodge horns when dodge was 12 volt for a few years. They really have a nice tone, and strong motor that works winter or summer without re-tuning it. Read the label at swap meets, they are around
 
The horn resistor that goes inside the horn will burn out eventually and could become a fire hazard. The one that mounts to the frame is large enough (watt wise) to handle the current.

I ended up rewiring my horn and it works fine. Not quite the same as an original on 6 volts, but close. Now if I can just get the horn button to work consistently.
 
The armature is the limiting factor since is can't be rewound for 12-volt. A 12-volt armature would have to be fabricated to get the 12-volt to sound more like the old 6-volt but a rewound field will get it relatively close.
 
When all else fails...my 6 volt horn burned out on my 12 volt system. I bought a new 12 volt horn from A&L before they quit selling to the public, but you can still buy one from the major suppliers.
 
I saw an A once where the guy had made a horn resistor from a bendix spring. You sure would never burn that thing up. He mounted it inside the frame near the steering box. The horn sounded pretty much like it did on 6 volts.
 
Pete said:
I saw an A once where the guy had made a horn resistor from a bendix spring. You sure would never burn that thing up. He mounted it inside the frame near the steering box. The horn sounded pretty much like it did on 6 volts.
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I've also seen a few times, a Bendix spring being used to run a 6v starter on 12 volts. Personally, I prefer to convert the starter internally by reconfiguring the field windings. Easy but it takes a while unless you buy the new field windings from a vendor but the ones I bought a while ago didn't have the right curve to fit the inside of the body and so, shorted to earth. That was a very inconvenient no go. We were about 2,000 miles from home. Grrr.
 
Synchro909 said:
.... a Bendix spring being used to run a 6v starter on 12 volts. ....
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Synchro I saw a lot As in Australia with this set up , but can someone explained how it can possibly work ... I am incredulous.... the resistance of the spring must be about 0 ohms .... welding wire with its high resistance being used I can understand, but a a strip of spring steel? Surely not?
 
Lots of Model T's use the Bendix spring in series with the starter motor when converting to 12 volts. It does not take much resistance when you are talking the amps required by the starter motor. I think that the impedance is a factor too. The coil will restrict the inrush current. Adding a soft iron core could help.

For the Model A, the Bendix spring could be added anywhere, even in the ground cable for the battery. It would be out of sight. The resistance is negligible for the normal charging and electrical loads.

Steel has higher resistance than copper. I would question the Bendix spring use for the horn because the horn does not take that much current. To measure the resistance of the Bendix spring, you would need to push through about 100 amps and then measure the current using a shunt and the voltage across the spring. Then calculate the resistance using Ohm's law.
 
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nkaminar said:
Steel has higher resistance than copper. I would question the Bendix spring use for the horn because the horn does not take that much current. To measure the resistance of the Bendix spring, you would need to push through about 100 amps and then measure the current using a shunt and the voltage across the spring. Then calculate the resistance using Ohm's law.
Click to expand...

One would have to be quick, as the Bendix spring heats up the resistance goes up.
 
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