the problems could be related or could be seperate
obviously check the light switch in the door and see if it has continuity with an ohm meter.
the dimming of lights and rpm drop indicates a very good power drain, it is not a short but sounds like the power window motor is siezed or something. The dimming of the lights is a large current drain.
A good start would be the wiring diagram, identify the wires for the door light switch and test them in place. with the door closed it should show infinite resistance with it open it should show no or low resistance. if the resistance does not change then it is possible the switch is gone. take the switch out and jump the wires to see if they cause the light to go on.
as for the window motor check the wiring diagram and see if the leads connect to the coil of the motor. if so then that should be close to zero resistance if not it is a possible bad motor in that window.
Hope that helps