Coil Polarity

[plyfor]

Found this little dwg. on the net for checking coils polarity other than the conventional lead pencil test and the vendors' tester. No specificity for 12 volt neg. vs 6 volt pos. systems.

[Big hammer]

I've been thinking about why the coil polarity is important!
A spark is a spark at the plug!
I think I know but the experts hopefully will chime in.
My shade tree experience says it's the gap in the distributor first then at the plug?

[Tom Wesenberg]

Chicagoland mg club has the best explanation I've ever seen.

http://www.chicagolandmgclub.com/tec...neral/574.html

[plyfor]

Thanks Tom, wondered if or where the dwg. came from. A few paragraphs down, it says there's no difference in connecting the test leads to read the analogue meter for + or - ground systems ( even assuming the coils are marked + or - but also assuming as taught by theory that electrons flow across the battery from + to -).

[plyfor]

With neg. ground (12 volt) , one would think the + meter lead in sketch would be connected to the plug, not the head. The current path through the 12 volt - grnd.. coil would assume to be from + to - across the coil primary..

[Tom Wesenberg]

Ideally the lead to the plug is negative, no matter which battery post is ground, so the negative meter lead should always go to the plug.
I like to use a high ohm resistor between the meter leads, so I can short out most of the high voltage, rather than sending it through the meter.

[plyfor]

Our 12 volt ( negative ground) coil terminals are marked; so in summary, the ignition switch red wire is the ground leg and goes to the neg.coil terminal. The black wire runs from the + coil terminal to the + j box terminal.
Would assume since the coil is marked that no polarity check would be required.

[Mitch]

That is correct