Ignition Switch Wiring Question


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Old 05-09-20, 07:25 PM
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Ignition Switch Wiring Question

I have to replace tractor ignition switch. Old switch was 3 posts, 3 position:
B battery
S starter
I ignition (coil)

New switch is 5 posts, 3 position
B battery
S starter
M magneto
L lights
G ground


Im assuming magneto and coil ignition are different. So on the new switch i would connect B with battery, L with ignition and s with starter.

With ignition coil the coil gets 12v all the time or the engine would shut off. A magneto only sees a short duration of 12v, or it would burn. So the M post on new switch doesnt see constant 12v. However the L post gets 12v all the time so it can be used in lieu of an "I" designation on the switch.

Is my thinking correct? I just want to confirm so i dont damage the coil or something.
 
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Old 05-10-20, 05:24 AM
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I think your idea of using the L for ignition will work. I would check the switch contacts with a multi meter just to confirm that each contact is doing what you want.

Magnetos don't receive electricity from anything. They are connected to the crank through gears it generates the power for the spark (it's a small, high voltage generator). There is a grounding wire that turns the magneto off by shorting to ground. The magneto position on the switch might be closed when the switch is in the off position shorting the magneto killing spark. Then when the switch is in an on position the contacts for magneto are probably open.
 
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Old 05-10-20, 06:57 AM
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As Pilot Dane stated, you have to check the make or break status of switch terminals for each of the 3 switch positions of the old switch to determine if the new switch can duplicate the switch terminal status for its 3 positions. Are the old and new switch positions OFF/RUN/START?
 
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Old 05-10-20, 11:46 AM
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Hiccup when trying to start. I am not sure if its related to switch since I have been doing other stuff.

Turning the switch on give 12V to + of coil as I intended. I also have voltage on the negative side of voltage depending if the points are pushed in or not. However, when I crank the engine I get voltage drop on both the positive and negative side. I removed the iginition wire from the switch and jumped the coil directly from the battery and I was able to get it started a few times and then it quit doing it all together. Now I have no spark.

I got some hunting to do unfortunately.
 
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Old 05-10-20, 12:38 PM
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There needs to be 12v+ on the + side of the coil. The negative side is pulsed by the points.
What did you connect the ignition wire to on the new key switch ?
 
 

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