I would use a light oil. 'Three-in-one' is a popular oil for home use in the UK, and is on sale in most supermarkets.
If your drivers side door won't open, try spraying some WD-40 into the area where the door connects with the lock inside the car. This will lubricate the lock.
I had the same problem with my 1996 tahoe, the best way I have found is to get a can of PB BLASTER penetrating oil. Then spray the lock mechanism on the door and let it sit. Then try working the lock from both the manual lock and the remote. If that does not work, you may have to remove the door panel and lubricate the lock linkage from the inside of the door. BE Careful removing the trim piece on the door handle, it will break easily. It's a good idea to spray all of the locks and mechanisms on a regular basis to keep them from sticking. ANSWER You could have a weak door lock solenoid that is not fully moving the unlocking mechanism.
Then the rods that connect to it must be messed up, lubricate everything inside the door as they must be frozen up from rust.
The best way to test a door lock is to locate the wiring for the door lock usually in door boot or kick panel. Use a test light with a probe and poke each wire until the door lock is activated. How ever be sure to they are not vacumm locks
Check if the fuse for your interior lights isn't blown. On many cars the Door Ajar light will come on when there's no power to the interior lights. The dashlight then grounds itself through the interior lights. It depends on the car made. for example Taurus, just lubricate(real good) the lock with wd40, will take care of the problem. some cars have sensors will lock automatically when you close door then will LOCK automatically. if one of the locks is jamed the ajar warning come on. Easiest way lubricate all doors lock you will fine. Good luck
Undoubtedly a deadbolt lock is one of the best. Also using locks with a ANSI Grade 1 classification is always best.
you need to take the outer skin off and lubricate the lock
There are a number of reasons why your door might not lock. You could have something stuck in the door for example.
Things to check, is the release all the way in? Lubricate the lock, WD40 or similar. Adjust the lock up if needed. After you lubricate the lock mechanism, cycle the hood release cable a few times, so that the lubricant penetrates. Continue to lubricate the mechanism at least once every few months to prevent future sticking of the cable.
you go here for the best walkthrough. http://www.talkford.com/topic/131866-how-to-change-the-drivers-side-door-lock/ hope it helps
If you have a garage door that has a lock engaged and you try to use an opener to get the door to go up, the motor (opener) will still try to engage and move the door into the up position. The motor and the lock will be fighting against each other and could damage your door. It could also damage the lock. If you have an opener on your garage it is always best to remove the lock. A garage door opener acts as a lock on it's own so it's unnecessary to have both.