Power windows, Silver Shadow 11

My power windows on my UK market Silver Shadow 11 have been problematic of late, first the rear passenger window stopped working, then the front passenger window quit working and then they all gave up. I removed the door cards and cleaned all the wire and switch connections and now the driver's window and front passenger window work using the driver's door switch. The rear left passenger window works from its door switch but not from the driver's door switch and the front passenger door switch doesn't activate the window motor. On testing the front passenger switch I find that there's 12+ volts on both contacts before I flick it, once I flick the switch the voltage stays at 12+ on one side and drops to zero on the other side but the earth wire simultaniously becomes live at 12+ volts. Just wondering if any of you more accomplished electrical gurus can tell me if this is normal, electrics definitely isn't my forte but an earth wire turning live when the switch is pressed seems odd to me. I know that the window motor in the front passenger door is OK because it works from the driver's door switch, I just can't figure out why it won't work from it's own door switch. Also, I can't figure out why the rear left passenger door switch will raise and lower the window but the driver's door switch elicits no response from the same motor. I've cleaned every wire connection except the B-post earth (which is difficult to access) but the earth connection looks clean with no sign of corrosion. If I take an earth reading between the motor earth and the car body there's continuity. All the micro switches seem to click when pressed and spring back when released. I think I'm overlooking something obvious that would be easily spotted by an auto electrician. Any advice would be much appreciated.