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John Deere L120 Lawn Mower will not engage blades.

Was cutting grass and then noticed that blades were not turning and cutting grass. The lawn mower blades will not engage when PTO switch is pulled up. I bought a new switch for the seat and replaced it, but that did not resolve the problem. I disconnected the PTO switch and checked resistence on the pins. The pins are in three rows labeled Com A, Com B, and Com C. When I checked these pins Com A and Com B was reading around 1.0 ohms. Com C has been getting very erattic readings 22.0 ohms and higher at times. Thinking it may possibly be the PTO switch. Another thing that is unusual, is after replacing the seat switch, I tested the seat switch to see if mower would turn off if I got off of the seat. The mower kept running after I got of the seat, and I did not have the parking brake engaged. The mower should have shut down if I am not mistaken. Not sure what to do right now.

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5 Answers from these members:
afritz afritz
I understand that your lawn mowers blades are not engaging. While you are waiting for an expert to respond, I have attached some helpful links below that may provide information to assist you with your question. Have a great day!
by afritz afritz Earned 1,258 community points in Lawn Mowers
May 12th, 2012
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Manage My Life
the reading on Comm C is on the switch with all wiring disconnected. All readings are from the pins on the pto swich.
by Manage My Life
May 16th, 2012
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Jerry C
Hello Michael,

Comm A and B are probably standard contact switches and when closed act like a piece of wire, electrically. I am also assuming that the reading from Comm C is coming through a solenoid that has resistive load due to the many feet of thin wire that it is constructed from.

I look forward to your reply,

Jerry C
by Jerry C Earned 317 community points in Lawn Mowers
May 16th, 2012
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Manage My Life
is there any reason why Comm A and Comm B has a reading of only 1.0 ohms, while Comm C has a reading around 22 ohms. I have gotten higher readings on Comm C.
I will check the color of the wiring at the contacts and let you know soon. Thanks for responding.
by Manage My Life
May 16th, 2012
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Jerry C
Hello Michael,

First of all, I appreciate the troubleshooting that you have already performed. I can verify that you should not be seeing erratic ohm readings on any of the connections at the pto switch. The switches in the circuit are either open or closed and the solenoids should show a steady ohm reading. The 22 ohms that you read would be typical of this type of solenoid.

Here

is a link that I was able to find to the actual wiring diagram for your tractor.

If you would determine what color wiring is at the contacts that you mentioned as A, B and C, I would be happy to assist you in determining where the fault is. I would say at this point it is a connection issue of some sort, wiring or internal to a switch or solenoid.

The seat safety switch is a good indicator that there is probably a damaged area in the wiring harness itself or one of the switches in the circuit has failed. However, you may want to check to be certain that the switch hasn't been inadvertently depressed in it's housing.

I look forward to assisting you with this problem.

Jerry C
by Jerry C Earned 317 community points in Lawn Mowers
May 15th, 2012
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