ok then this is not an scr controlled lift, it is contactor which means its either on or off.
What this is telling me is that there may be a setup issue possibly in the machine settings making it think there is a potentiometer or something in the settings has gone out of calibration.
If you go into the setup menu there will be a calibration routine you can run to get the system back to normal operation.
Yes even with switches the Curtis system still wants some sort of input to register settings for this function, the switch setup just has an invariable setting it registers which i supposed has changed for some reason.
do you have a service book on this unit with the calibration routines?
You'll need this to calibrate the traction and hydraulic function. Check with your local Yale dealer and see if they can get this information for you, they might sell you the service book for a nominal fee.