Engine L120 will not turn off

[sandtrotter]

I have a John Deere L120. It will not quit running when I turn off the key. I have checked the following.
The ignition switch is connected and the cutoff sensor under the seat is connected.
It starts and runs fine....it just will not shut off. While running I have even unplugged both the ignition switch and the sensor under the seat and it still keeps running....so I have been unplugging the two spark plus wires to shut it down. I don't see any loose or disconnected wires anywhere. I could sure use some HELP..........

 

[bertsmobile1]

The Kill wire is a ground connection.
Check the ignition switch, some that are mounted into plastic have short ground wire on the ignition switch as a stand alone connection so it is also a fall off alone and without being able to connect the M ( Magneto ) & G ( ground ) terminals you can not turn off the engine.
For the same reason, if the small wire on the coil falls off the it can not ground the coil and it wont turn off either.
Pull the blower housing, check you get continuity between the kill wires to the coils & ground when the switch is off and open circuit when the switch is on.
A little care here because if that wire gets battery voltage it will cook and they ain't cheap.

 

[sandtrotter]

Thanks for your help. I'll get right on that.

 

[sandtrotter]

Well. After messing around for quite awhile I was able to determine the kill wire that travels to both coils had no continuity. I was going to fabricate a replacement but upon closer inspection I discovered that there are small resistors implanted at the yoke (where the wire splits to go to both coils). I called a lawn and garden store that services and sells JD mowers and they could not find the part on their schematic. I went to JD's website and found it difficult to navigate.
My L120 is a 2003. If anyone knows the part number I would appreciate a shout. Thanks

 

[bertsmobile1]

by no continuity I hope you mean no continuity to ground when the engine is turned off.
When running that white wire should be open
When stopped it should be closed.
What you saw were diodes to stop the kill wires interfearing with each other when they fire the coils.
They are not resistors as such.
It is a Briggs part not a JD part so not shown on the JD parts breakdown but is shown in the wiring diagram in the technical manual.
Follow that white wire wire to the engine plug , usually behind the starter, disconnect the plug and check the mower side for continuity.
If it does not go from closed ( off ) to open ( on ) when you turn the key then either the ground to the switch is bad or the switch itself is bad or the white wire is broken.
If you need to mow right now you can run a jumper from the kill wire up to the drivers position and ground it against something metal to stop the mower which is a touch easier than racing around and yanking off the plug leads.
Reach up behind the ignition switch and pull the plug off.
It only goes on one way so no problems putting it back on but to be on the safe side leave the engine harness disconnected till after you refit the ignition switch plug.
On the ignition switch plug there shout be a white wire and that should be the other end of the white wire at the engine plug.
measure it for continuity. engine plug to ignitions switch plug.
If that is OK then measure continuity between the black wire ( Ground ) on the ignition switch plug & ground.
If that is good then the switch itself is duff. Double check this by testing the M = Magneto ( white wire ) terminal & the G = Ground ( black wire ) terminal on the plug.
Open for on closed for off.

You will find it easier if you toss a rope over a rafter with a very heavy weigh on one end & your ankles on the other.

Search the site for John Deere manual I think there is a linke to a location with a download of the L 100-L150 technical manual. otherwise buy one from JD it will pay for itself the first time you fix something & don't have to take the mower to a shop.
Written so a 5th generation intermarried hillbilly can understand it

 

[sandtrotter]

Ther problem was the wire going to both coils was bad. I found a used one at a local logging supply outfit that does small impliment repairs. Cost me $5.00 US
Went home. Installed it, and BINGO. It works. All systems go!
Thank you for headin me in the right direction. Overall cost to repair. One bad attitude for awhile and $5.00.