It could simply be the master switch, or it could be a shorted/broken wire. First thing to do would be to take the switch out of the door panel, get a test light or voltmeter/multimeter, and test whether or not you're getting voltage sent when you press the window switch. If not, then you know it's the switch. So the right rear doesn't work from the master or it's separate switch? Could be the right rear switch, or it could possibly be the motor. Once again, check if voltage is getting sent when you press the switch.
You can get replacement window switches from
http://www.gmpartsdirect.com They are much cheaper then my local dealer. Highly recommend them.
I'll try and get a wiring diagram up if I can tomorrow afternoon.
TOC Admin
Brando