the water from the over flow messedthe unit up, blown the fuse you see at the top but also form the look of it got into the unit and also rusted the plug. . . swaped the unit that only bolts to the coolant bottle by two bolts then had to cut off my plug (yours could be ok) and wire ina new one. fiwed the fan staying on which was got as it used to flatten my battery!
reason for my overflow was the head was on its way out mate....