Why does the power door locks on a 2001 Blazer only work with the remote entry not with the door switches?
Generally on an F-250, if you have power door locks and a keyless entry door pad on the drivers side door it should be equipped with a keyless entry remote. You can also put the vehicle into program mode by using this procedure: Cycle the ignition from off to on eight times within 10 seconds ending in the run position, if the door locks cycle it is equipped.
Deprogram the remotes, if at all possible. The remote entry module also controls the door locks themselves (If you leave the rear door open when you lock the door, it won't lock... so the REM will re-lock the doors after you shut it.), so you can't simply remove the remote entry module or you'll lose all power lock functionality. The module is located behind the radio.
What would make the power locks on your 2004 Grand Marquis stop working using the door mounted switches but still work with the remote control?
Start with looking in your owners manual. Take the key less entry fob into the car with you. With your key, turn the ignition on and off eight times. Do not start the vehicle. The door locks will start to cycle lock/unlock Press the lock and unlock button on the fob until it locks and unlocks the door by its self
A more or less permanent (though difficult) solution might be to remove the door panels and disconnect the lock actuator wire connectors on the offending locks. Though if you have the door open, you might want to fix the locks instead. If the motors keep running but otherwise work OK, the solution might be to check and clean the limit switches. Alternatively, you might need to replace the door lock actuators. For a quick way…