Small Engines (Lawn Mowers, etc.): John Deere 314 Mower, john deere 314, electric clutch

Question
I have a hand-me-down 1984 John Deere 314 lawn tractor.  After it runs for a while with the PTO engaged (5 to 10 minutes) it stops running while the PTO is engaged. It acts just like a saftey switch has been tripped. It will still run fine with the PTO switch in the "off" position.  It is an electric clutch (I believe).  I bypassed all the operator present and drive safety switches to rule them out and replaced the ignition switch (for other reasons as well). Any suggestions on what to look for?

Answer
Here's a long shot.  I called a buddy and he recommended checking the battery, more specifically he recommended cleaning the terminals and battery cable ends with a wire brush.

Apparently the clutch draws a lot of current.  If the battery and the alternator can't keep up with the load the clutch needs then you can loose the 12v DC for the coil, which generates the spark and the engine shuts off.  

He also said that the clutches on the 318, very similar to the 314, short and cause similar problems.  You can check the clutch voltage with a volt meter...it should be around 12.8 volts DC with the clutch engaged.

Let me know what you find.
Eric