I have got in the past ignition coil overheating, making the engine run very erratically and in some cases it even wouldn't run at all until the coil got cooler. In one occasion I changed the coil for a new one and it overheated as well.

Isolating the problem by excluding heat transfer from the engine, bad grounding and + feeding, bad condenser or break points, what other things could cause this?

I have read about: wrong timing, wrong spark plug gaps, dirty spark plugs (not in my case), poor fuel/air mix.

  • can you do a waveform capture of the primary current ramp and secondary ignition on the coil? or take measurements?
    – Ben
    Commented Apr 7, 2017 at 21:41
  • Can measure with a halfbreed digital multimeter? Commented Apr 8, 2017 at 0:36
  • You'd need a dedicated secondary ignition kV probe setup, you can probably catch current ramp on a multimeter if it has a min max function. Honestly though a waveform capture of the secondary ignition would tell you what was wrong or where to start looking.
    – Ben
    Commented Apr 8, 2017 at 3:33

1 Answer 1


Had this a long time ago when some car ignition systems (Alpine, Solara, Horizon) which had ballast resistors in the supply to give 9v (which were bypassed for starting with 12v) - when a 9v coil was used in the wrong system it would overheat.

  • Correct, if the 9V coil is fed with 12V. In my case, the first one was plain 12V and overheated, then the other I tried is 9V with resistor, correctly hooked, still overheated. Commented Apr 8, 2017 at 0:36

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