1989 Buick Century passenger side rear window will not go back up. All other windows work fine. I checked the switch in the door by exchanging it with the rear driver-side door, so I know the switch is good.

could be where the front driver door bent the harness wire could be cut.

Motor which runs when u press the switch has loosened connections or is not functioning
Get it checked

i have fixed this problem on mine remove front drivers door panel trace your ground wire from window switch and make sure you have a good ground once you fix your ground you will fix your windows

You most likely have a bad window lift motor or MORE LIKELY a broken window regulator. The door must be disassembled to replace either or both of these.
It could also be a bad window control switch or a broken wire in the door-jamb area. Please note that EITHER of the switches for the passenger window (the driver's control switch or the one on the passenger door) can cause BOTH of the switches to not work to move the passenger window. In this case, electrical diagnosis must be performed to locate the cause of the problem.

probably needs new switches (in driver's door panel). if window is ever left down while raining, switches will quickly corrode.

Check the front window solenoid, and the window switches to see if your getting power to, and out of the switchs.

CHECK POWER WINDOWS 20 AMP CIRCUIT BREAKER.

NEED TO CK IF THERE IS POWER TO THE SWITCH, CK IF SWITCH IS LOSE , INSIDE DOOR PANEL ,CK WINDOW MOTOR,RUN IT DIRECT TO TEST THAT THE MOTOR IS IN RUNNING CONDTION ,

Replace the Driver side window switch. These have a corrosion issue.

I've had a similar problem with my 2003 Buick Century. In my case, the driver's side front window one day went up and would not come down. I knew that the switch was malfunctioning by sticking in the up position since the window continued up despite the fact that Iet off the switch when the window was half way up and it continued going up. I had to pull over and pull the master switch assembly from the door panel and unplug it to prevent the window motor from being damaged by the constant power feeding it after the window was up. Basically, it would have burned the motor out. I cleaned the switch and it now works fine most of the time. I still need to replace the assembly. Not sure this is the reason in your case. I would check the back window and see if it goes down with the switch on the back door panel. If it does, then you are having problem with the master switch assembly on your front door panel. Moisture from rain from the window being down during rain or dirt may have corroded the switches' contacts.