It is on the multifunction switch, there are two different switches, one is w/rear wiper and one is wo/rear wiper. If you can't see the switch or it looks different from the one in the picture maybe the car had the switch replaced with the wrong one. . See the switches at the link below.
Ask people at Junk Jard - they are professionals in their business. In most cases they will tell you you which car is suitable for donation. Also, before you install the old switch, carefully dissemble, clean and lubricate with electric lubricant or Vaseline. It will help to prolong the life for forever. Good luck.
For the most part, there's only 3 things that control the wipers. Your switch on the steering wheel, power to the motor and the motor itself. There are other variables but if you get a Chilton manual and study up on the wipers, it'll give you some direction to go to troubleshoot your problem. It's not unusual for the motor to go bad.