Thanks to all. Unfortunately the steps retract with the switch in either on or off.
Does it make a difference if the ignition is on or off? Ignition on, or running, and the steps will retract with door closure regardless of wall switch position.
Are you at all mechanically inclined? Own a voltmeter?
If your step has not been replaced, it probably is a Quikee, and their wiring is very consistent across the models. Mine is a Quickee, if I am wrong about general fitment there should be a chorus soon.

Page 9 has a decent step troubleshooting procedure. They say you need the 4-pin connector to troubleshoot, it does help. Crimp on barrel connectors on 16Ga wire worked for me.
Easier yet, and more directly related to your issue: You can unscrew the switch from the wall, and see if there is 12V on either terminal. If you look at the link I sent, on page 10 there is a diagram. You will see the 'hold open' switch is fed by a '5-6 amp fuse/breaker (not supplied). If there is no voltage at the switch, there is a good place to start to see why it doesnt function. If there is, check to see if the switch is working correctly. If that doesnt solve it... full troubleshoot might be in order. If the wire from the switch to the step controller broke/corroded apart at a butt connector/ corroded internally and signal isnt making it to the control unit, it will do what you are describing. A continuity check from the step connector to the switch might answer the question also.
If you find no voltage at the switch, you can make a jumper wire and feed both the wires on the back of the switch with 12V+. This would give the same input to the control unit as 'wall switch on' and keep the step out. Put a fuse inline, or (redneck warning!!

) use only a few strands of the wire as a 'test' contact in case there is a short down the line. The couple strands of copper will be a 'fuse' and melt before anything else does. If the jumper works, you will KNOW it is either the switch failed or the power is not getting to it.
Good Luck!