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With a magneto the purpose of the manifold switch and ground wire is to ground (disable) the magneto when running in diesel mode. This is to extend life of the mag breaker points and the spark plugs. Consequently the manifold switch contacts OPEN to enable the mag when the decompression lever is set at the “start” position. With a distributor however the opposite action is required. The manifold switch must CLOSE its contacts when the decomp lever is in “start” to complete a circuit feeding battery voltage to the coil/distributor for starting. Therefore manifold switches are not interchangable between magneto and distributor-equipped engines. ----- Sounds as if your mag is not making a spark. Try removing the grounding wire from the mag, then test the mag to see if it makes a spark. (Pull a wire from one of the plugs, stick a spare spark plug on the plug wire you just removed, then crank and see if you get spark.) If you don’t get a spark the problem’s in the magneto. And there's a good chance cleaning the breaker points will fix it. However if you do get spark either the mag is timed wrong or something else is amiss with the engine.
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