Check the switches you have for normally open or normally closed, they you can diagnose the ones on the tractor with a volt/ohm meter. If you have a infrared heat gun, that would be a plus.
I have come to the conclusion that the JD sensors are not the best. Not sure who they are sourcing them from (CHINA) but it has cost them a lot of money. I replaces 4 hydraulic sensors (myself, 5 under warranty) on my 8310R, and have had a three other sensors replaced by a JD tech in the field. The last two that were replaced had plastic threads and were over torqued from the factory. You are suppose to be able to clean them (wheel speed sensors that are magnetic and will collect wear materials), but he could not screw them back in as the threads were distorted. Lovely!