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Discussion Starter #1
Murray 405011X92A
B&S 219707-0300-E1

Been working all afternoon on this mower for a neighbor of mine. The starter motor turns the engine over just fine, but the engine doesn't fire because there's no spark. If I unplug the engine from the chassis's main wiring harness, it'll crank right up & run like a top, but then you have to pull the wire off the spark plug to cut the engine off since you then have no way of grounding out the coil. The kill wire at the engine is fine, so I think the wiring harness must be grounding out somewhere, but I can't figure out where or how.

I removed the 4 safety switches and checked their continuity with my electrical meter. They all seemed to be okay, so I reinstalled them. At least the NO switches test with the meter as open when the button isn't depressed and closed when it is. The NC switches test as closed when the button isn't depressed and open when it is. I tried to visually inspect as much of the wiring harness as possible, and I didn't find any bare places on any of the wires. However, there were quite a number of places I couldn't get to to get a good look.

The owner did tell me that when they first tried to start it yesterday, the battery seemed to be weak after sitting for about a week, so they jumped from a good car battery. After messing with it for a while this afternoon, the battery got weak and I charged it back up. After that I removed the spark plug and connected a spark tester to keep from continually running the battery down.

It seems to me that the spark is getting sent to ground somehow either through the safety switches or through a short circuit that I can't find. I haven't figured out how to analyze the ignition key switch to figure out if it is working properly.

I've noticed that there is a loose wire coming out of the seat switch that has a connector on the end. On the wiring diagram it says that this is a factory test connection and isn't used in the mower assembly. Can I somehow hook my electrical meter to it to test the circuit integrity?

So, that's where I am right now. What should I check next and what procedures to use to isolate the problem? I've studied the wiring diagram until I am cross-eyed, but still haven't figured out how to find the problem. Any help or suggestions would be greatly appreciated.
 

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Discussion Starter #3
I finally figured it out this morning. All it turned out to be was as corroded connection along the wire that leads from the DC output from the stator to one of the safety switches. I just cleaned out all the dirt, crud, & corrosion from the connection & the engine fired right up.
 
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