f620 ztrac John Deere mower blades stop turning

I have a f620 zero turn John Deere mower- when I turn the PTO switch on the blades will come on and run for about 2-3 mins and then they shut off- they stop turning- even with the PTO switch still on the blades still stop turning- right now they will not come on at all- I have changed the fuses- with a test light I have power to the blue wire that runs to the PTO clutch- but I'm not sure about the ground wire not getting any ohm reading- can someone share some insight