Is it possible to back up a single magneto ignition system using an electronic system on the same spark plugs rather than having to change to two plg heads?

  • 2
    $\begingroup$ Possible, or legal? Certified, or homebuilt? $\endgroup$ Nov 6, 2019 at 18:07
  • $\begingroup$ Are you wanting to do this just from a redundancy standpoint? $\endgroup$
    – Ron Beyer
    Nov 6, 2019 at 18:29
  • $\begingroup$ What do you do if the single mag somehow fails a cylinder in a shorted manner? Or if a plug gets fouled and stops firing? That backup system on the same mag will no do you any good. Stick with 2 plugs per cylinder. $\endgroup$
    – CrossRoads
    Nov 6, 2019 at 19:37
  • $\begingroup$ It's a BGA registered TMG. I'm just looking to back-up the magneto in case of failure but without the complications of replacing the cylinder heads (which I agree would be the ideal solution).. $\endgroup$ Nov 6, 2019 at 21:23
  • $\begingroup$ The spark plug is a fairly minor part as an ignition failure risk factor. Far more likely on the primary side or at the coil. So dual source to single plugs gets you probably 80% of where you would be with dual plug heads. In the Corvair world, it's theoretically possible to modify the heads for dual plugs, but is considered not worth the trouble considering the other failure modes introduced by making more holes in the head. If you rummage around on William Wynne's site for a bit you should be able to stumble onto sourcing for the ignition diodes. I'm pretty sure he sells them. $\endgroup$
    – John K
    Nov 6, 2019 at 21:27

1 Answer 1


For a homebuilt or ultralight, yes. There are high voltage diodes that take a high tension lead from 2 separate sources with a single output, made for racing, that allow you to run a single plug from either of two sources, whatever they are. They are popular on Corvair aircraft engine conversions. You can run a mag and battery system together, or two battery systems, or whatever, with a one-or-the-other ignition switch.


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