i have a mondeo mk3 estate ghia x and the drivers side passengers rear door will not lock or unlock with the remote i have taken the door skin off and messed with the wires but no joy any help thanks.

 

It could be the central locking control unit (or ECU). If the actuator and mechanisms in the door are all OK it could be that causing the problem. I've got exactly the same thing with a MK3 estate but on the drivers front door. ECU sits up under the dashboard, and are about Ł20 on good old eBay.

 

Take both rear door cards off, and check the pulses on the working door lock, see if there are the same pulses on the other rear lock, if the pulses are there the lock is buggered.
Test with a test LIGHT not digi meter.
tabetha