My easy way to replace the lock actuator in a 2001 Ford F150, Driverside.
This may not be the "proper" way but it has worked on both my passenger side and now the driver side. And I can do them in about 15 mins.
I guess the motors in them just get weak and won't lock or unlock the door. When I opened the old ones up no gears were broke and it all looked good.
Step 1: Gather Tools
Ratchet with a 10mm socket (Or a wrench)
Looooooong straight blade screwdriver
Small straight blade screwdriver
Oh, and the replacement actuator.
Make sure to roll the window to the UP position too.