When we bought the MH steps wouldn't work, 2 days and I had the steps off, AS was to blame for not welding all four of the bolts only three nuts came off easy 4th had to be attacked from the step well. Motor was frozen with corrosion because they used a rear window electric motor from a ford taurus.
This time I tried to repair motor from under the MH but working on my back it wouldn't reinstall, had to take whole step unit out and reassemble. First time no sound and dead motor this time it chattered but couldn't find the stop position. Tried the spare computer switch module and it didn't stop the chatter on open step. Found the plastic rollers in the gear box were oval instead of round. Replaced with new rollers and it worked.
Motor off is determined by the extra power it discovers on reaching the end of motion. Oval rollers didn't allow it to find a fixed stop.