Before you spend too much more time on a power check, you need a wiring diagram. To see if the override switch is a power shut-off or a signal interupt, to cut the signal from the door switch and stop step operation that way.
Was the over ride working with the old steps ?
Can you get ( download ) wiring diagrams for both sets and compare them ?
I'm on the road for the next week, no internet I'll get back on ASAP.