Fairbanks-Morse Mag switch wiring

[914pete]

Anyone have a simple diagram for wiring a simple mag switch? Fairbanks-Morse Model PE1-2B7E-2. 32hp Casler cut case. Suggestions for the actual ignition switch? I could also use a manual for this little 1/2vw.

[Richfroh]

The purpose of the magneto switch is to ground the p-lead to disable the mag. The switch should have continuity to ground with the switch in the "off" position and should be open with no continuity to ground with the switch in the "on" position.

[Dan_]

The screw post you show in your pic should be connected to the primary side of the mag coil.  (p lead)  If the mag housing has continuity to ground you should be able to kill the engine with a screw driver in contact with the mag housing and the screw post.  You can buy a button on a metal bar that does just that as a Harley kill switch.

Any good quality single pole/single throw switch could be used.  You will want a guard on the switch so that it cannot be knocked into the off position, or use a regular aircraft key switch.  Also you want certainty that the wiring cannot inadvertently get grounded.  That could be really bad if you are over hostile terrain --no restarts.

A wire connected to that screw post and one side of the switch, another wire coming off the other side of the switch to ground should do it.

If the wire breaks or the switch fails open the mag is hot.  That is why you never touch the prop unless you consider the mag hot.

[914pete]

So if there's no ground wire attached to the p-lead, as shown in the picture, the mag is hot? I should get spark if I turn it over? The p-lead needs to be grounded to something to be cold?

What type of wire makes a good ground and where should I ground it to? The engine mount? Fuselage?

[Dan_]

To be able to talk on a radio get this wire, ground the shield on the engine end only...  https://www.aircraftspruce.com/catalog/elpages/edmotefzel.php?clickkey=6369

Download on wiring...

Install it like this: https://www.eaa.org/videos/50864529001

Aircraft qrounding:  https://www.eaa.org/eaa/aircraft-building/building-your-aircraft/while-youre-building/building-articles/electrical/electrical-grounding  https://www.experimentalaircraft.info/articles/aircraft-electrical-power-ground.php

MIT level course in aircraft wiring: (be sure to click on grounding)  http://www.aeroelectric.com/articles.html

[914pete]

To be able to talk on a radio get this wire, ground the shield on the engine end only...  https://www.aircraftspruce.com/catalog/elpages/edmotefzel.php?clickkey=6369

Download on wiring...

Install it like this: https://www.eaa.org/videos/50864529001

Aircraft qrounding:  https://www.eaa.org/eaa/aircraft-building/building-your-aircraft/while-youre-building/building-articles/electrical/electrical-grounding  https://www.experimentalaircraft.info/articles/aircraft-electrical-power-ground.php

MIT level course in aircraft wiring: (be sure to click on grounding)  http://www.aeroelectric.com/articles.html

Thank you, Thank you, Thank you Dan!

[914pete]

Thanks for the responses. I'm trying to learn as much as I can about this little 1/2vw before Frank finishes my prop. I have been setting it up on a run stand. So I wasn't getting a spark from my mag and figured out the ground post was shorting out on the mag case. I removed it and added some new plastic washers to insulate it and now I'm getting great spark from both plugs. I ordered some shielded wire from ACS per below and made a nice P-lead and added a toggle/kill switch. Now, hopefully not too dumb a question, both plugs are sparking at the same time. Shouldn't they be sparking independently?

[Dan_]

Both are supposed to spark... A wasted spark every other stroke.