Failing implies it works sometimes.
Most step issues are associated with low battery and corroded ground wires - either/both will make the step act like it's possessed.
Given the age of your rig -- clean the ground wire connection to the step - do the same for the house battery and your chassis battery. Also check the connections to your house battery and clean those as well (wire brush) so they shine like new. Also lube the step .. forum search feature likely has lots of posts on that subject.
Hope this helps.