Thruster not working

[tspco]

Ok I have a simple thruster model I downloaded from the warehouse.
It works great with a slider the ui code is -(0.5-slider("thrust"))*4000, with nonautofreeze ticked on.
I tru to replicate this with my own model, it doesn't work, fact is the slider dosn't even show up. What the heck am I doing wrong?