I am about to start this same project on my Deere 3520. Two questions for those who have done this.
1. Do you find it difficult to disconnect the quick couplers due to residual pressure in the lines, when you remove the grapple? It seems to me that these type of E/hydro valves will hold pressure in the A and B ports in the neutral position, obviously desirable to secure a load between the grapple, but not desirable when disconnecting QD fittings. I could see the need to shut the tractor down, then cycle the valve to relieve line pressure before disconnecting the lines. Or I'm thinking of maybe adding some type of pressure relief to the lines if this is necessary. I believe the new Deere compacts that have the solenoid controlled 3rd function have a pressure relief tee handle on the valve base presumably for this very reason.
2. I've read that the solenoids on the valve can burn up the contacts in a plain switch due to fairly high amperage and some type of reverse high voltage charge that occurs when the switch is released and the solenoid closes. My understanding is that using relays and a diode between the +and- side of the solenoid will save the switch. I didn't see any mention of this with your setup and I'm wondering if you've had any problems so far?
Thanks