I'd check the fuse box for any sign of corrosion and re-seat any fuses having to do with window operation. The switch likely used is a 'double throw, double pole' type with a center rest. This type allows switching the polarity of voltage supplied to the motor to produce both directions and without the car's wiring diagram, it's difficult to tell you which terminals need to be shorted to move the window in the desired direction.There is probably a connector inside the door that completes the path to the car's electrical system and if this has gotten wet, it may be corroded and become intermittent.
For this problem and as a guide for other problems to come, I recommend investing in a Haynes service manual which will contain all the electrical diagrams you need to find this problem and very complete service info on the engine and drive train as well.It would be the best $25 you can spend and may save you thousands in the future:
'98 Regal manual You can buy them on line or in most auto parts stores.
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