My central locking works intermittently and states drivers door open and most often will not lock it. Any idea? 

door pillar switch comes to mind first, if switch is dirty or u/s then interior light stays on ?

Locate the switch - possibly with a rubber cover over it, press in and out, if interior light goes on and off then switch is ok and probably suspect the locking system in the door itself.

Fortunately i haven't had this problem.... yet ! Mk6 fiestas probably have the same issue so worth a look in that section.

I think the interior light is controlled from the door "closed/open" microswitch in the door lock assembly, and if the central locking thinks either of the front doors are open, then the car cannot be locked.  First check is the multi way connector on the "A" post.  It is a bayonet fitting, remove it, check for any corrosion, and replace ensuring it is fully secured.

I had this on our Fusion, with the alarm also going off occasionally, and ended up changing the door lock motor, which is qute a palaver, door panel off, door handle off, inner panel off, diconnect window glass from winder assembly  etc.  Haynes manual is good, but it might give you a bit more room if you remove the door loudspeaker.

Topic below is for a rear door on a Fiesta, may help

 

 

Another thread that might help

I had the same problem, only solution is a new door lock mechanism. It's annoying as the switch is a separate part rivetted on and they should supply the switch on it's own , it's a rip off.

Just managed to sort the same issue on my 1.4 2009 Fusion. Changed lock with a second hand one. Improved for a few days but came back with same intermittent issue. Ended up getting a whole new door. As not the same colour as car had to gut it and swap the interior door card as a whole. Been a couple of days with no reoccurrence. Strongly believe my particular issue was the wiring in the door.