Question: what is the difference between a 6 volt coil and a 12 volt coil?
Answer: You need to connect an amp meter in series with the coil and 6 volt battery. A 6 volt coil will draw 4 amps. If you have an accurate ohm meter, reading across the posts of a 12 volt coil should be about 3 ohms. A 6 volt coil is about half of that.