electrically,  about all I unhooked  was  that low pressure sensor, filter restriction sensor, and the 4  solenoids.  
I did   'clean up'  about a foot worth of  scotch lok type  butt connectors/splices  and was careful to make sure  green and black from the  sending unit went to green and black on the harness...  and  re-tucked all that wiring back up in a neater  fashion.

Very possible  there's a pinched wire.   I did use  zip ties to  hold everything in place.   and there's a lot of  bends in that harness  as it's snaked along.

Everything works  perfectly,  AFTER the computer is  'booted up'.  

I've found that  after starting the engine,  I only have to  pull out on the  fuel shut off to slow the engine down to  barely running... and the  hydraulic pressure drops.   (THIS IS WHEN THE WARNING LIGHT GOES OFF!!!)   just the opposite of what's normally seen!    Soon as the light 'blinks' back on,  Everything is good to go -   except for that  warning light being on.

When the next rain  halts  haying,  I'll  pop the  computer connector off, and   ohm out  those 2 wires  end to end.