I have a switch on the alternator field circuit on my race car. With the ignition on if you throw the switch the indicator light I have on the switch flashes very bright, and you get whacked on your finger. I'm no electrical eng. but it has to do with a DC inductive field collapsing like a coil, the winding are the alt field winding.I could probably wire it differently(than the way I came up with)but we just don't touch the switch anymore. It's ok to turn it off and on before the ignition. But if you turn it off with the field energized you get whacked.