M post on ignition

[cbouch]

I understand that if I connect 2 wires, one each from the m lugs on the ignition switch to to one each of the points it shuts the engine down when the switch is in the off position...I did a continuity test on both m lugs and found that when the ignition is off there is continuity between the lugs...when the ignition is on there is no continuity..so my question really is when you connect both sets of points together does it effectively ground them and shut the engine down just by the fact that you connected them together or does a ground wire somehow come into play? Thanks

 

[GA_Boater]

What are you working on?

Not knowing - One of the wires is probably ground and when the switch is off, the ground through the M lugs is grounding the ignition. Often M stands for Magneto and mags are grounded to shut the motor off. Like I said, this is without knowing what you are working on.

 

[F_R]

If you are working on a common twin cylinder with magneto, yes the connections you describe are correct. Connecting both sets of points together via the switch kills spark on both cylinders.

If you wonder about the grounding, suppose #1 cylinder is about to fire. It fires when #1 points break. But your switch is connecting #1 to #2 (Off position). #2 is grounded at the time because #2 points are closed. Not only that, #2 is seeing only about an Ohm to ground through it's coil's inactive primary winding. #2 is inactive because the flywheel magnets are over passing by #1.

Same scenario, but reversed, when #2 is about to fire.

 

[cbouch]

Thanks very much...I should have stated the engine that I was working on. It is a 1955 evinrude 25hp. I now understand how it works..by connecting both sets of points together it shuts the engine down because at any point in time one is closed and grounded and because they are connected via the m lugs on the switch they are both grounded.

 

[lindy46]

Someone has correctly installed that ignition switch. Originally, that motor had a push button to start, and a choke button to kill the motor.