Here is that engine's illustrated parts list:
http://bsintek.basco.com/BriggsDocumentDisplay/Z6ntACVJ1DajI.pdfHere is the operator's manual:
http://bsintek.basco.com/BriggsDocumentDisplay/flivAJX-nfBhU7y.pdfIt was manufactured on 13 October, 1988, so of course it has Magnetron ignition, as you said. The Magnetron has only two wires coming out of it: the thick high tension lead to the spark plug, and a longer, thin black wire with a spade connector on the end of it. This is the kill wire. Usually the kill wire is also connected to the Magnetron by a spade connector, but it may be hard-wired at that end. The kill wire normally runs to a contact on the governor plate above the carburetor. On most models, this contact touches the speed control lever on the governor plate when the speed control is set to minimum. This shorts the kill wire to ground, which stops the spark.
The kill wire works by grounding the internal part of the Magnetron that corresponds to the moving point in a points system. That makes the module function as if the points are not opening and closing, so there can be no spark. Hence, running the kill wire to either a momentary switch or a normal on/off switch, the other side of which is grounded, is a safe and effective way to stop the engine. I would not recommend the use of a momentary contact switch, since that would leave you with no way to disable the engine except disconnecting the spark plug. This creates a risk that at some time, someone will accidentally start the engine while working on or around it. However a toggle-type switch, that will remain in the ground position once set there, is suitable.
Remember, the kill wire must not be connected to a non-zero voltage. There have been many reports of Magnetrons being destroyed by ride-on mower tenants who connected the kill wire to the +12 Volt terminal on the starter switch, instead of the switchable ground terminal.
