Bought a battery powered horn for a buck at an antique store and the thing works! I run twelve volts and dont want to do any damage to it. Can I use a lantern battery or is there a resistor I can use?
Check online, there are companies that make devices that drop 12V to 6V. Whatever you decide to do, keep track of what you spend on the workaround so that you don't end up spending more than the cost of a new 6V horn!
A properly working and properly adjusted battery horn will draw 5 amps from the nominal 6V system. You need to drop 6 volts to make it work OK on 12V. To do that you need a high power resistor that is about 1.2 to 1.3 ohms and you can buy an ignition resistor at NAPA that will likely work since that is the ohmic value that is somewhat commonly used for ignition resistors that are in series with ignition coils. You must NOT honk the horn for long or the resistor may overheat. Short toots will work just fine but beware of long parades and horn honking since the resistor will get very hot.
Dont suppose you happen to have a part number John?
Go to Auto Zone and buy this:
It has two resistors in one unit, use your multimeter to pick which resistor best meets John's 1.2 to 1.3 ohm spec. If neither is exact, try the higher resistance to be safe and see how the horn sounds.
Make sure you don't guess about the value since if the resistor is lower value than 1.2 you could smoke the motor winding as well as the resistor. Some auto parts stores only tell you what car and not the value. Napa carries Echlin and an Echline ICR11 or ICR11SB are both 1.35 ohms which is probably a good value to use if your T is using an alternator and likely to thus have a much higher voltage than simply 12.6 when charging the battery. If you do need a 1.2 ohm then the ICR23 by Echlin will give you that value. To be totally authentic for a model T then of course you need to go with whatever is the cheapest low quality part you can find and I think that the ICR11SB is probably an import but I can't be sure
I have a 6 volt Schwartz horn on my Touring and have a Model A coil in the hot side wire. It works as a resistor and drops the voltage. I simply cut the hot wire and connected the wire to each side of the coil primary and mounted it under the floorboards. Works great. The horn is a little strong but for short bursts it is fine.
I guess the engineer in me is forced to point out that inductive loads are very hard on electrical switches and the horn button is a switch. The battery horn motor is an inductor and also has points in it. Using additional inductance as part of a voltage dropping resistor just makes the horn button contacts and battery horn contacts arc that much more which shortens their life. Points on the T coil arc when the current path is broken and the contacts in your horn and horn button will do the same when you honk your battery horn. They will arc even more severely if you add inductance in series with the inductance that is already there in the motor. The primary of a coil certainly will act as a voltage dropping resistance but the inductance it also has is undesirable. A normal power resistor is a better choice if you have it available.
Why not convert your car back to 6 volts, then you won't have to worry about anything! I've got a '25 with all new wiring and a great starter switch, and it spins over like a 12 volt, and you won't have to worry about damaging your bendix.
Its a great idea larry. My mag doesnt work and I really dont want to pull engine