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Coil Polarity

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  • Coil Polarity

    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.
    Attached Files

  • #2
    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?


    • #3
      Chicagoland mg club has the best explanation I've ever seen.


      • #4
        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 -).
        Last edited by plyfor; 11-24-2017, 09:25 PM.


        • #5
          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..


          • #6
            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.


            • #7
              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
                Mitch commented
                Editing a comment
                That is correct

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