Kill Switch on a Magneto Ingition

[HokieMS]

I recently bought a Gravely L8 walk behind, for brush cutting in tight spaces, and steep hills. I need to install a kill switch for safer shutoffs back on the handle bars. I can do basic wiring no problem, and have the switch I want to use. However, I'm not much of a engine guy I've never had an engine quite this "vintage", so this is a new one on me.

My question is this: what do I ground out to kill the engine? Currently, I can short out the post coming out of the magneto to the case of the magneto, and it kills the engine. There was a metal strip to push into the magneto case, or I can use a screwdriver to contact both parts, to kill the engine. So my thinking was to run a wire from the magneto post, through a switch or a normally-open momentary contact button, to a chassis ground. My feeble brain assumed this would work. I checked with my multimeter, and the chassis, post, and case of the magneto are common. So.... how in the **** does shorting the post and case of the magneto kill the engine, if they are common? Where does the switch need to be wired to to make it kill the engine, when in the "closed" position? I've looked online, but can't find obvious pictures or diagrams explaining it. I'm sure it's something simple, but I can't make heads or tails of it.

Thanks...
Mark

 

[V1Rotate]

The way to kill an engine is to ground out the magneto. Are you sure that the post that sticks out of the magneto is common to the rest of the machine? It must be insulated or the engine would get no spark.

 

[Redneck in training]

The coil between those two contacts has low impedance for DC so it will look like a short. Shorting the coil will kill the engine. That is my guess.

 

[HokieMS]

V1Rotate: yes, it is definitely common. I bet I checked it 50 times, it really had me stumped. :laughing:

Redneck: Hmm, that could explain it. I clearly don't know much about the magneto internals. So, any simple switch should be sufficient to close the circuit from chassis ground to the magneto post?

 

[TC 40 Chuck]

you've got it with this post. any switch that will ground the 'post' coming out of the magneto will work well. try not to rotate (when tightening the nut) the threaded 'post' coming out of mag when you install the wire going to the switch. Redneck in Training has the right idea on the internals of the magneto.
Good luck!

 

[jaotguy]

kill switch is an old tin can with a plastic top and a small piece of chain ....

connect the "kill wire" to a chain ( bead pull chain , drain stopper chain ) in the middle of the tin can lid ...

mount the can so the chain hangs straight down ... and attach it to the metal frame of the beast ...

if the unit rolls over or on its side, the chain should touch the side of the can and short out the ignition ....