Having some somewhat similar problems. Background, machine is a Deere 7775 that I got without a motor. It already had 3 "override" switches in the cab, assume for seat belt, parking brake, and another, seems to lock out boom. A friend of mine swapped in V2003T out of a large commercial mower into it and fabbed what was needed to get it in. Got it back and it had been working great! A while back once, it died on me. I don't recall, I may have put the boom lock on. Used it Thursday, no issues. Stored outside as usual, and it poured Thursday night. Went to crank if Friday because I have a semi coming to my house in 20 minutes to unload and WOULDN'T START. Display was VERY dim, then eventually went out. I thought maybe dead battery so hooked that up, no difference. After "fooling around" with a bunch of different things, I was able to get it started in "service mode". Flip it to run and it would die. Start back up in service. Eventually after trying that 4-5 times it stayed running in run and used it for approximately 30-45 minutes. Turned it off, and now won't start again for nothing - doesn't even crank. Panel is now bright as before, so assume maybe fuse had bad connection or something. There seemed to be an F 04 or P 04 message on there when it fired up the 1 time. I checked all the fuses in the engine bay, seemed fine, but i replaced all anyway. I replaced the black 5 pin relay with one from auto parts store, no change. There is only 1 row of fuses in the overhead, not 2 as shown in the book, but they seem fine. If I turn the 3 override switches to the "other" position, the dash beeps so I assume those override circuits are still functioning as intended. Can't see an easy way to even reach the starter to try and either hit it to see if it is stuck or manually override solenoids and see if it will run if i hot wire it. Thoughts on where to go next? I don't care about safety things, came from an old Case that didn't have any from factory

If overriding the dash will get this thing usable, I'm all for it. Hauling this without it being able to load itself on a trailer sounds difficult, and i'm waiting to hear back on the backlog from a dealer since the Deere place around the corner only does "green", not "yellow". Fearing the modifications that have been done are now going to come back and bite me as they will likely bill me 5 hours for trying to figure out whats going on with 'fixes' applied over the years...