Might help us to know what model of windlass you have. I would think yours has a worm drive so if it's truly turning and it's not the clutch slipping it has to be moving hydraulic fluid through the motor. This means there is an issue with the valve system where perhaps the spool in the valve is not returning to the off state. This seems unlikely to me though.
Pics of the windlass and valve system would help as well.
Lindell 36, Twin 370hp Cummins