Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Here's my next attempt.

The black side of the Reed switch contact has current or at least continuity to it. The white side does not but will once the contacts touch thus sending whatever current the black lead carries back through the white wire to wherever it goes. If the red lead went to the opposite side of the Reed switch, bringing the points into contact would simply create a direct short, which I suspect would not be good. Still, the polarity of the red lead must go somewhere useful, or you cannot have any current flow through the system.

Now I must wonder, what polarity from the battery pack is ground, and is that the same as the black lead going to the Reed switch?

I suspect that you should want the polarity of the ground and the live wire to the Reed switch to be opposite polarity so that then the power transmitted to the white lead by the contacts in the Reed switch would then be able to power the spark against the grounded spark plug.

Hope any of that made sense?