Do you still have water in the fresh water tank? If not, add some and see if the pump will pump fresh water. If not, then the problem is definitely with the pump or pump electrical circuit, not the FreezeGard system. I too would not add antifreeze to the fresh water tank. I would blow the system out with compressed air before I did that.
If the pump does not run at all, then there is a pump or circuit problem. Winterize switch should not prevent the pump from running, in either position.
The FreezeGuard system works great on my 5er.