There are two wires, but maybe only three ends exposed; two of four ends becoming one for connection = three. One wire is wound clockwise, one is counter clockwise. The switch chooses which of two is active, the brushes do not change orientation. (The other way to reverse a motor is to have one field wire and change the brush positions instead)
If you cannot make it change direction it is possible there is a short between the two fields (usually youd just have one side fight the other, but how much would depend on the points along lengths of the short.)
