You will need a test light, take out the switch that does not work , put the key in the on position and check for power on one of the wires comming out of the switch, after you find the power going in you need to check the other wires while moving the switch one wire has to change from ground or power to power or ground, depending on if the switch supplies ground or power to the motor. . if one of the other wires changes then its probably the motor. there an easy way to check the motor is to take off door panel un plug the motor connector, take the connector on the motor side and ground one side and power the other using a jumper from the battery. if the motor moves it works. if there is no power to the switch trace the wires throught the harness, using the test light probe wires about every 1inch or so until you get power once you get power you know the short is between there and one inch bak, just splice in a new piece of wire (solder the connections) and you should be good.
Sorrry if this is so long,
Hope it helps...Peace