mondeo central locking - meke
1999 mondeo when i try and lock my car it is not working, sometimes it will lock with the key on the passenger side only never the drivers side . any ideas what it could be
mondeo central locking - Waino
The same thing happens to mine - if you search the threads on this site, you'll find a reference to it.

The problem seems to be caused by either a dodgy electrical connection or some sort of stiffness in the passenger-side door mechanism through under-use. I read somewhere that a stronger spring can be fitted to the motor/mechanism - but I don't know the details. I squirted a liberal quantity of WD40 into the lock and it seems to work occasionally now - so my plan is to use the passenger side door lock more frequently in the hope that it loosens up. I'm reluctant to remove the inner door panel as it's usually a recipe for breaking bits off.

The situation with mine is that, if you lock the car from the driver's side, it immediately unlocks - but if you manually lock the passenger door from the inside first, then the car can be locked from the driver's side using the key.
mondeo central locking - oldpostie
My 1999 Mondeo was a great car, but the troubles with the central locking playing up were one of the reasons for getting rid of it.