This is a function / feature that's part of the keyless entry system - and can be turned on or off.
The steps to activating/deactivating the Autolock feature are detailed in the Owners Manual. See "Related Questions" below for online source of Owners Manual
I don't know how standard the steps are across the different models and years of Ford/Mercury products - but try these steps (I got them from a 1998 Sable or 2001 Windstar).
Activating/deactivating autolock with the keyless entry system
Before following the activation or deactivation procedures, make sure
that the anti-theft system (if equipped) is not armed, ignition is off, and
all vehicle doors and liftgate window are closed.
# Enter 5 digit entry code # Press and hold 7/8 control # Press and release 3/4 control while holding 7/8 control # Release 7/8 control.
The horn will chirp once if autolock was deactivated or twice (one short and one long chirp) if autolock was activated.
To re-activate autolock, repeat steps 1-4.
A key is needed to enter, lock, and unlock many Mercury Sable cars. A key is also needed to start the engine.
Sometimes it is correct but not all of the time. Its worth a try.
It tells you the doors are not locked. The light goes out when you lock the doors. It's just a friendly reminder to lock your doors.
Your Ford/Mercury dealer can get the code. See "Related Questions" below for instructions on changing the lock cylinder
In a 2001-2003 Mercury Sable, the door lock relay is typically located in the interior fuse panel, which is found underneath the dashboard on the driver's side. To access it, you may need to remove a cover or panel. Refer to the vehicle's owner’s manual for the exact location and identification of the door lock relay within the fuse box.
If you remove door panel you should have access to unit
You will have to take it apart to determine why it's not working then you can fix it.
On my 1992 190E I can lock the trunk with any of the keyed locks. If you lock the doors, the trunk locks and if you lock the trunk, the doors lock. In other words all the keyed locks are electrically interconnected. In reality the locks are not electrically interconnected. There is a pump in the right side wheel well of the trunk, it uses vacuum to lock all the locks and pressure to unlock them. Although the pump is powered electrically, the locks are not.
replace the lock actuator (motor)
call a lock smith
Might e be time for a batteryMight have lost its programmingSee "Related Questions" below for more about both
if the doors do not lock then one of the fuses is out!