I have a 950, had the same problem. You will find you have two safety switches, one on the PTO to make sure you can't start engaged, and the other on the range shifter. Over time, the connectors got funky with intermentent contact and did the same thing. I cut off the connectors on both ends and used a butt splice to hook up the wires, no more problems. I cleaned them several times, but it always came back to the same problem. Removing the bad connectors and hard wiring solved the problem for good. The switches themselves seam to be reliable. Also, something to look for is the contacts inside the selonoid, these are rebuildable. The plunger is about $30 or so and has a copper washer attached to it. The contacts are less than $5 ea, you will need 2 of them. Replacing both gives you a new switch inside the selonoic. After disconnecting the battery, remove the 3 screws on the cover, remove the plunger, and look at the contacts. Sometimes you can just clean the contacts and you are good to go. Hope this helped,
Chris