I was gifted the remaining parts of a height-adjustable desk from a family member. The surface of the desk was being re-used for something else, and the control panel (keypad) was non-functional. That had suffered from either a dog bite, or a child bite, we'll never know. Either way, the bite had severed what I later found out was the trace to GND.

The control panel was straight forward as you can see from the pictures, domed contacts pulling 1 of 5 lines to GND, and from the behavior I surmised there was a pull-down inside the brain-box - which I decided not to explore. This was easily tested. Short GND to each of the 5 wires to see what happens. Sure enough, the desks motorised functions still worked. Pretty easy to use some PULL-DOWN GPIO's on a micro I thought.