This is not like a car as there is not anything to plug into for the diagnosis of the pto system. This is the usual old school type system. Power goes from the pto switch to the manual /auto switch and then to the solenoid valve unit under the right side o the tractor higher up under the platform. Does the pto switch red light glow when pushed in? That's a starting point to check. I also put my mode switch in the manual position as that bypasses the rocker switch on the 3pt hitch lever. Let us know what you find.