UPDATE 11/13/22: I've been able to get the engine to throttle up when attempting to engage the lift or fwd/rev drive functions. However even though it throttles up the lift and drive functions are still not working. If I use the lower control unit (lift UP) I notice that it starts to lift but does not continue after an inch or so. I noticed the hydraulic fluid is just above the minimum level so I am wondering if that could be the reason. Plan on adding some hydraulic fluid as soon as I figure out what particular fluid I should be adding.

I have an SM3884XT and likely have the schematics for this scissor lift.
I have the same problem. The equipment runs but fails to lift or drive forward or backward using the upper console. It was functioning a year ago but was showing the problem intermittently even back then. Recently (11/4/22) I started it up and it failed to drive or lift using the joystick. It will still steer but I notice it no longer increase the throttle when I push the blue engage button when I have it switched to either lift or drive. I'm thinking some sort of solenoid is refusing to engage that throttles the engine up. I think the steering still works because I don't think that requires the engine to throttle up like the drive or lift functions do.