The problem might not be entirely electrical. I removed the below Regulator and Motor from the passanger side rear today. You could run the Window up but not down and when you pressed to go down the motor would not go at all. (What I found was that the Window Regulator Mounting Plate is bent and Regulator Gear Teeth deformed from running on an angle.)
In my case the Motor is not grounded through the through the Chassie. I tested the Motor by swapping the + and - wires from a battery to the 2 wires comming from the Motor (+) to the Green wire and (-) to the Black Wire brought the Window Down;swapping them would raise the window.

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84 300D, 82 Volvo 244Gl Diesel