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No RPM drop on left mag

dahugo

Member
My ignition switch should be wired right BUT I get no drop on left mag at run up. How do I troubleshoot this?
 
Disconnect the "P" leads from both mags. Remember that both mags are now "HOT". Do NOT turn the prop.

Check with an ohmmeter between the "P" leads and ground.

In "both" position, neither P lead should be grounded.
In "left" position, only the right P lead should be grounded.
In the "right" position, only the left P lead should be grounded.
In the "off" position, both P leads should be grounded.
 
Easy way to check

I was taught to periodically test the mags for proper grounding by briefly turning the mag switch to off and then back on immediately prior to shutdown. This test should be done at idle power.

If the engine continues to run normally, you've likely got a bad P-lead ground circuit.
 
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