Front Passenger side window won't go up; only down

I have replaced the regulator and got the same result. I then replaced the master switch (I read somewhere if it's bad, neither switch will work and got the same result. The window only goes down (can't go down any further so you hear the motor come on briefly). I switched the front passenger switch with the rear passenger side switch since I knew it worked and got the same result, just to rule out that the front passenger switch is faulty. What's left? Wiring? I wouldn't think it's a fuse since the other 3 work fine. Please help. It's especially frustrating.