HOW CAN I UNLOCK MY 2004 LINCOLN LS? SLIM JIM...RESET KEYLESS ENTRY???

Your keylles code is located in the label on Security Module. To find it, open the right/rear door and pull the on-body weatherstrip slightly away from the body at the rear side of the door opening. Fold and lock the right/rear seat back down into the locked position.

Carefully pull the trim panel that houses the seat belt height adjuster and anchor pivot off of the body. Now carefully pull the lower trim panel from the inside outward far enough to expose the VSM (Vehicle Security Module). This module has three electrical connectors plugged into it, coloured green, grey and blue.

On the module is a label bearing a number similar to 4L2T-15K602-EA. On the same label will be FIVE large numbers. Those five numbers are your five digit keyless entry keypad code.

Additionally, if you have some "new" key, could try to re-programed and synchonized, you must have all remote entry transmitters (maximum of four) available before beginning this procedure. To reprogram the remote entry transmitters:
1. Ensure the vehicle is electronically unlocked.
2. Put the key in the ignition.
3. Turn the key from the 1 (LOCK) position to 4 (RUN).
4. Cycle eight times rapidly (within 10 seconds) between the 1 (LOCK) position and 4 (RUN). Note: The eighth turn must end in the 4 (RUN) position.
5. The doors will lock, then unlock, to confirm that the programming mode has been activated.
6. Within 20 seconds press any button on the remote entry transmitter.

Note: If more than 20 seconds have passed you will need to start the procedure over again.

Hope this helps (remember to rating this answer and leave a testimonial comment).