Rear door lock help

[Falcoron]

My 2004 Alhambra won't lock at rear door the mechanism does not close onto the keeper bar. I got another lock from a working one but that doesn't work either the door closes but it's just sitting there unlocked and could flop open when driven as nothing is stopping it from doing so. Is this a usual problem and can it be fixed, anyone know how too please

 

[90landrover]

Is this a mechanical or electrical lock I.E. do you blip the key or do you use the key to lock it. If it is an electrical lock I would check the cables going from the car into the door ( op left hand corner of door when it is open). These are thin cables and have a tendency to break after a while.