Mk3 foucs rear passanger lock and window problems

Hoping someone can help. Have a 2012 focus titanium powershift. The rear passanger door suddenly stopped unlocking sporadically. I then noticed the window was also not working when door wouldn't unlock. Checked the wiring. Seemed OK but pulled it out and tried a new loom as advised but no change. Then tried another door control unit still no change. Have noticed now the window switch flickers and comes on and off. The switch on the drivers door is solid. Neither make the window work smoothly. Kind of moves in small increments and sometimes not at all. Only noticed switch as was working in dark so probably been doing that from start. Tried disconnecting and reconnecting battery. 

Any advice would be helpful. Not sure where to head next. Was thinking maybe earthing problem but not sure if the rear door has its own earth point or what colour wire is the earth. I miss normal wiring before bus systems and computers. 

Really would appreciate any advise. Still sporadically unlocks or sometimes doesn't lock. 

Thanks for any advise. 

Robin.