sounds like a bad sensor or damaged wiring?
or maybe just incorrect sequencing when activating these sensors (switches)?

the hip support sensor just sounds like an operator presence switch that activates the system when closed.

the footboard sensor could be a high speed trigger switch and should only be activated when the truck is in motion. If you activate it before you start driving it will do nothing, you will need to open the switch and then close it again while moving.

i would check the sensor inputs at the card and see if your getting any signal from the sensors, if not then check the wiring, if you are then sure, the curtis unit may be damaged.

i'm just making educated guesses here i do not know this truck so....
try this and see if that helps