Coils positives and negatives

[bob46320]

I think that what Ray has said is correct. The down side of getting the polarity wrong is that the High voltage will pass through the Low voltage winding. In effect, a coil is like a transformer, but with only 3 connections. The low voltage winding have a + and - end (irrespective of earth polarity). However the high voltage coil has one end going to the plug and the other end connected to one end of the low voltage coil. If the wrong coil is used. then the return from the high voltage winding will as I say pass through the low voltage winding which is not designed for the elevated voltage (The difference between 6 volts and 10,000 volts or so). Some coils will not take this overload and fail at some point.
Correct me if I am wrong, but aren't coils pulsed DC, not AC ?