I recently replaced the window relay in my 300SD, now driver's side window works, and have discovered the rear driver's side needs a regulator. Neither window works on the passengers side of the car. I was driving the car last night and noticed that the switches for the left side (the windows that work) light up but the switches for the left (don't work) are dark. What sort of issue am I looking at here?

The car is a 1984 300SD W126.120

Thanks!

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In the Garage:
'84 300SD, 85K "The Princess"
2011 BMW 328I XDrive, DD