Tractor Repair: 4555 three point, diagnostic port, cab air

Question
the lift arms on my 1989 model jd4555 (cab & air) will not lower. when the lever is moved to the lower position, the arms go down just a tiny bit and then stop.

Answer
The 55 series  is jd first attempt at electronic hitch controls. I will try to steer you in the right direction but if gets over your head electrically then you might need a service call from your local dealer. On the rockshaft arms the is a little arm that is connected to a potentiometer it tells the computer where the hitch's position is. Check to make sure that arm/rod is not broken. Make sure that the wires to the two solenoid's on the back of the rockshaft valve are not damaged. A quick test of the solenoids are to swap them. One controls up and the other controls down.Make sure you swap the spools also. They are the same so they can be swapped that is if you can get them off without breaking them. If it still does not work then under the cover where the fuses are you need to put a fuse in the diagnostic port it is in the lower right hand corner with a arm like the rockshaft, turn on the key and on the dash it will flash codes. Write down the hcu codes and send them in a follow-up question. Then if you are up to it, I can see what else we can do.