Been some chatter lately about the ballast resistor and why its needed. Even I was not very clear on it. Take a look at this youtube video. Not the same as the N wiring but pretty darn close, same principles apply.
What this guy is saying is that a 12 volt coil can not take 12 volts without frying (after an undetermined amount of time) same with the 6 volt. So why call it a 12 volt coil? Guess we can't have everything in life but that explains the resistor need.