"Not so, grasshopper!" To anthropomorphize things, every time the mag points open, the collapsing field makes a current run down that wire to the switch looking for a path to ground. When it gets to the open switch (mag "on") it turns around and runs back to the high tension side and fires the plug. While all this is happening, a magnetic field builds up around the wire and then collapses. The shielding is to prevent this field from escaping into the real world and interfering with your radios. (Non-electric, assumed NORAD planes typically didn't have or need shielding; excess weight.) You'll need shielding from the mag to the switch housing. The switch itself should be shielded too, alternatively it can be enclosed in a metal box to which the shield is also connected.
John > > Theoretically, a ground lead should not have to be shielded, > because all > shielding is is wrapping a ground coaxially around a positive > lead. So the > shielding on a ground lead should, I said SHOULD be redundant. > > That said, part of shielding is to ensure that the path to > ground is as low > a resistance as possible. Any high-resistance path to ground > WILL radiate > noise. So by providing a greater surface area (radio > frequency likes big > surfaces), > a more efficient ground is provided, hence the noise gets > shorted out, rather > than radiated. >
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