Doors lock when put in drive but won't unlock when put in park

I have a 1999 Mercury Mountaineer
When I put the truck in drive the doors lock but when I put it in park door's won't unlock?
If it's a relay where would it be located? If not what would it be.

Have you checked your Owner's Manual? There's a lot of good, often overlooked, information in there. If you don't have a paper copy, go here (https://www.fleet.ford.com/maintenance/owners_manuals/results.asp) and check the Index for Locks -> autolock.

-Rod

I read the manual, I did the lock unlock programming but still no luck with the doors unlocking after driving and then park, is there any else i can try?

I have a 97 mountaineer, and my doors have never unlocked when it is put in park. Im not sure ford made it to do that, although i may be wrong, and if i am then i have to get my door locks looked at also.

The owner's manual states when the autolock feature triggers, but makes no mention that it ever unlocks the doors. I believe the way the feature is operating for both of you is as designed.
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Autolock is a feature that will automatically lock all doors when:


all vehicle doors, liftgate and liftgate window are fully closed
the ignition key is in the ON position
you shift into or through R (Reverse)
the brake pedal is released


The autolock feature repeats when:


any door is opened and then closed
the brake pedal is released

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You should be able to disable the autolock feature if it is a nuissance, but since using the door handle from inside unlocks the door it is not an inconvenience for most people.

-Rod