If like my 2002, all the switches are in the driver's door, except for one on the passenger door. I would suspect a broken wire in the harness that feeds thru the door gap. Since multiple switches are affected, I would suspect a common wire, which usually means a wire to chassis ground. However, I have never fooled with mine so don't know how it works. The switches could control the motors directly (like in my 1985 M-B), but my guess is that they are just digital requests to a body computer which controls the higher motor currents. Perusing the wiring schematic would tell. I replaced both window regulators in my front doors. As I recall, the motors have sealed connectors (Metri-pak?) so not easy to probe the voltages while plugged in. You would have to pierce the insulation.