i know it's been a few days since this last post was first posted.
if you've lost platform controls i would check the key switch that switches it from ground control to platform control, make sure it is actually doing that. If it is then back probe the circuit through the harness up to the platform control plug and make sure it is supplying the signal at the platform control box. If it's not powering that box on the unit will not function. While doing that check the scissor harness and make sure there are no chaffed parts of that cable, there are several parts that bend when raising and lowering and when they age those sections do tend to break apart, covering comes off, wires break internally etc.

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.