Small Engines (Lawn Mowers, etc.): PTO switch failure, switch failure, doide

Question
Hello.  I have a Craftsman Garden Tractor Model No. 917.275031 that is approximately 9 years old, I believe.  I have never had to replace the PTO switch (raises and lowers blades for cutting) until a week ago, when I pulled the red switch to engage blades, and the switch came off in my hand.  Looked like it had melted, but I assumed it was just worn out and replaced it.  Got through one cutting.  Next cutting, same thing.  the red portion of the switch came right off in my hand, appeared melted.  So perhaps something is shorting out in there to melt this plastic?  Any thoughts?  Thank you for any help you can offer.

Answer
Kelli
The reason that the Switch had melted is their is a short in the Clutch,this is a known problem with the sears tractors. What you have to do is unplug the clutch wire that goes to the PTO switch.I can think of two possible causes of burning out the PTO switch that quickly (#2 is most likely the cause):
1. The PTO is drawing way too much current. Disconnect the PTO coil and measure its resistance. The PTO coil should be about 4 ohms.

2. Look at the schematic in your owners manual. There will be a diode connected in parallel with the PTO coil. The job of that diode is to protect the switch from arching when the PTO is switched OFF. If that diode is defective or disconnected the PTO switch will burn out after a short number of uses. Find that diode and check to see that it is OK. I am not sure where the doide is located on your tractor, but maybe when you installed the first replacement switch the diode did not get reconnected properly.
To determine for sure if you are reading the resistance of the coil, or if you might be reading the inverse resistance of the diode it is necessary to connect the ohmmeter leads in one direction and record the reading. Then you reverse the ohmmeter leads and test the circuit in the opposite polarity.
A good clutch featuring a diode would read the spec of 2.4 to 2.9 ohm in one direction, but would read zero (or near zero) ohm in the opposite direction.
If the clutch is shorted, your readings will be low ohm, in either polarity.
So, you might have a shorted clutch, or you might be reading the diode.