If they stop where they are, check for the permanent live supply at the connector on the wiper motor, this is what supplies current after switch off.
If that is ok take apart the wiper mech on the motor, you will see a nylon wheel about 32 in diametre that turns with the arm, this has a dip in it where the switch rests when stopped(it cuts the circuit), check the wires have not broken on this.
This will be found behind the cover that is attached with rivetts, just use tie wraps afterwards with sealant around the edges to seal.
tabetha