Classic/Antique Car Repair: 12v to 6v model a horn, resistor, volts

Question
What is the best way to reduce voltage to 6 volts so I don't burn up a model a
horn?

Answer
There is a device sold on the market called "Volt A Drop" which is a voltage dropping resistor. I know it will handle between 15 and 20 amps. You will have to test your model A horn and see what amount of current it draws. The Volt A Drop sells for about 30 bucks, so you want to make sure it will handle the current without burning up.
Brad