I was ask to look at a rig they are putting together out of parts and pieces. The truck has a pto air operated pump 3 air lines 1 for pto and 2 that run a 2 way air cylinder up and down. The pump has a big line supply from the tank then it has 2 ports with the valve to hook a cable to limit how fare the bed raises. They plumed one port to the cylinder the other they plugged. When the pto is running with the switch in up it gos up then when the clutch is pushed in the bed gos down. How does it need to be plumed is the pluged hole a return line?
Sounds like a mess. Plugged port probably is for a return line, but from the sound of it, either there's a neutral spot for the control that's not being used, or a check valve missing in the pump, the bed should not be coming back down if you disengage the clutch or PTO.
Your up down air valve is 1, out of adjustment, 2 If your safety cable is hooked up too short, 3 The spool or the bore is messed up. Have you tried to move the spool by hand to see if you can find a position that will hold the box?
Muncie ? Chelsie? Red? blue?