Hello , I would check the wiring from handle
To plug those units were known to have broken
Wiring at the base of the joystick in fact Clark
Sent out a bulletin to remove the clamp at base of joystick that holds harness in place because of this issue I have replaced a lot of those small joystick harnesses because of this. Also check micro
Switches at base of joystick

I have worked on some of these trucks about ten years ago what l remember was that if you take the bolt out of the leg for the over head guard and swing the door open there is a factory wiring diagram on the inside after that remove the top plastic cover that is we're all the controllers are at l remember it used ev 100 for traction and to the right there was a green controller that was the controller for steering after that there is a black box with about 16 screw terminals on it that box was the inputs and outputs for the hyd controllers if any wire from the mast cable back to the box was not making it or a loose wire to any solenoid could be tilt sideshift reach the controll box would not allow the joystick to work.l would bet that there is a bad wire from the mast cable to the solenoid some were probably a ground wire.check all the wires from all the switches and the solenoid when the machine does not work back to the box and try to trace it down hope l was of some help.