The lock button on the passenger door doesn't work when the ignition is at "on" position.. only works when it's on "off".. is this electrical problem? :(

Do they work with the key fob, do you have one of those? They lock when put into gear an unlock when put into park because the BCM - body control module does that .

Door Lock System Components
The power door lock system consists of the following components:
• Driver door lock switch
• Front Passenger door lock switch
• Body Control Module (BCM)
• Relays: Driver Door Unlock -- on vehicles with RFA, Door Unlock, and Door Lock
• Door Lock fuse 15A
Door Lock System Controls
The power door lock system can be controlled by any of the following:
• A power door lock switch activation
• A keyless entry command -- if equipped with keyless entry


Driver and Passenger Door Lock Operation
When any of the door lock switches is pressed to the lock position, the BCM door lock/unlock signal circuit changes from an idle voltage of ~3.4 volts to 0.0 volts generating a lock command. The BCM then applies battery positive voltage to the Door Lock Relay, which in turn applies battery positive voltage to the Door Lock Actuator lock circuit of all the Door Lock Actuators. Since the Door Lock Actuator unlock circuits are held to ground through the resting Door Unlock Relay(s), the actuators execute the lock command, locking the doors.
The lock function can also be accomplished by the BCM having received a keyless entry door lock command, if the vehicle is equipped with keyless entry.


Driver and Passenger Door Unlock Operation

When any of the door lock switches is pressed to the unlock position, the BCM door lock/unlock signal circuit changes from an idle voltage of ~3.4 volts to ~1.7 volts generating an unlock command. The BCM then applies battery positive voltage to the Door Unlock Relay and the Driver Door Unlock Relay when equipped with keyless entry, the relay(s) in turn apply battery positive voltage to the Door Lock Actuator unlock circuit of all the Door Lock Actuators. Since the Door Lock Actuator lock circuits are held to ground through the resting Door Lock Relay, the actuators execute the unlock command, unlocking the doors.
The unlock function can also be accomplished by the BCM having received a keyless entry door unlock command, if the vehicle is equipped with keyless entry. Keyless entry personalization allows the driver door to be unlocked individually before unlocking the passenger doors. When this feature is active, the BCM will require a repeated unlock command to unlock the passenger doors.


Automatic Door Lock/Unlock
The automatic door lock/unlock function is a Vehicle Personalization feature with the following four programmable modes of operation:
The automatic door lock feature is disabled.
All of the doors lock when the vehicle is shifted out of Park with the ignition ON.
All of the doors lock when the vehicle is shifted out of Park with the ignition ON, and all of the doors Unlock when the vehicle is shifted into Park.
All of the doors lock when the vehicle is shifted out of Park with the ignition ON, and only the driver door Unlocks when the vehicle is shifted into Park.
For information on programming the automatic door locks, refer to Vehicle Personalization in Personalization.

All the other windows work ? Not a fuse , one fuse powers all the windows . Test for B+ voltage at the switch an the window regulator would be the proper diagnostic procedure . Do you own a volt meter ? know how to read a wiring diagram ? how to do basic automotive electrical testing . The Faint click you hear is probably a relay , which means the GEM - genaric electronic modual is energizing the window relay . The windows are computer controlled .

The GEM will activate the OTD Relay until one of the following conditions is met:

• The LF regulator control switch is pushed to the UP position.
• The LF regulator control switch is released (OFF position) and then moved to the down position (first detent) or one touch down (OTD) position (second detent).
• Seven seconds have elapsed since the OTD was initiated.
• A window regulator electric drive stall condition is detected on the one touch down sense line inputs.

The UP window operation is not controlled by the GEM. The feature is activated when the delayed accessory is active and the LF window regulator control switch is pressed to the UP position. The switch provides delayed accessory power to one side of the motor and ground to the other side through the one touch down relay. The one touch down relay is not active when the LF regulator control switch is in the UP position.
Passenger windows may be raised or lowered using the LF master control switches or the appropriate passenger window switch. Passenger window switches receive power when the delayed accessory relay is active and the LF remote lock-out switch is in the UNLOCK position. When in the LOCK-OUT position, the passenger windows are deactivated.
The GEM controls manual down and auto down window movement with the down window relay. The relay is activated by applying ground directly to one side of the down window relay coil, and deactivated by removing the ground signal.
The delayed accessory relay provides power for the operation of the power windows and the power moon roof. The delayed accessory feature is active when the ignition switch is in the RUN or the ACC position, or when the ignition switch is changed from RUN or ACC to the OFF/LOCK position and the LF and RF doors are closed.
The GEM will deactivate the delayed accessory feature when:

• the LF door is ajar and the ignition switch is in the OFF/LOCK or KEY-OUT position.
• the RF door is ajar and the ignition switch is in the OFF/LOCK or KEY-OUT position.
• 10 minutes have elapsed since the ignition switch was changed from ACC or RUN to the OFF/LOCK position.

Feature inputs:

• LF door open warning switch (open circuit with door closed, grounded with door ajar).
• RF door open warning switch (open circuit with door closed, grounded with door ajar).
• Ignition switch RUN position (battery potential on both the RUN and RUN/ACC inputs).
• Ignition switch ACC position (battery potential on the RUN/ACC input).
• Ignition switch OFF/LOCK position (absence of battery potential on the RUN, RUN/ACC, and START inputs).

The Trainer 24 Power Window Troubleshooting

Pull the door panel apart and check and see if the pun that locks and unlocks the door is connected, if so check the power supply the the actuator.

Sounds like the main wiring loom into the door has been damaged.
Check near the hinges, where the door swings, to see if any damaged wires. Does the door lock and unlock from the drivers side switch?

DEALERSHIP HAS TO RESET RADIO BUT YOU CAN REPROGRAM DOOR LOCKS BY CLOSING ALL DOORS.INSERT IGNITION KEY IN IGNITION SWITCH.ACCESS DATA LINK CONNECTOR ON DRIVER SIDE FASCIA JUMP DLC TERMINAL 1 AND GROUND TERMINAL 1 MAY ALSO BE GROUNDED USING DIAGNOSTIC EQUIPMENT CONNECTED TO THE DLC.SWITCH IGNITION SWITCH ON AND BACK OFF POSITION ENSURE DOORS LOCK AND UNLOCK INDICATING PROGRAMMING MODE ACTIVE.PRESS ANY BUTTON OF EACH REMOTE TRANSMITTER THREE TIMES WITHIN TEN SECONDS. WAIT 1 MINUTE OR REMOVE JUMP LEAD TO EXIT PROGRAMMING MODE.

Most likely needs to be re matched to the car.

Two bits of info off the net for you

C CLASS (1993-1997), E CLASS (1995-1997), SLK (1996-)
Procedure
1. Point the remote control at the receiver - this should be located in the driver's door handle or next to the boot lock button.
2. Press the lock/unlock button.
3. Within 30 seconds manually lock or unlock the vehicle using the passenger's door lock or the boot lock.
Alternative method
Procedure
1. Point the remote control at the receiver - this should be located in the driver's door handle or next to the boot lock button.
2. Press the lock/unlock button.
3. Within 30 seconds, switch the ignition ON.
Alternative method
Procedure
1. Point the remote control at the receiver - this should be located in the driver's door handle or next to the boot lock button.
2. Press the lock/unlock button.
3. Within 30 seconds, turn the ignition switch to position II.


and

1. Place key in ignition lock and turn to position 2 [all ignition lights on]
2: Turn key to off position and remove from ignition.
3. Within 10 seconds:
3a: press the Close [Lock] button and hold it down
3b: while the Close button is still depressed simultaneously press the Open [Unlock] button. Press and release the Open button 5 times [still holding the Close button down]
3c: Release both the Close and the Open buttons at the same time, and immediately push any of the two Open buttons once [i.e. either the Open doors or the Open Tailgate]

This information is for the resetting of a previously synchronised key to match the security system after batteries have been removed or replaced. This information does not work with new keys which it seems must be taken to a person with a key synchronisation device [or a super-ripoff-expensive MB dealer]

hope this helps

Try locking all doors and with the key unlock the front passenger door and reach across to the drivers door and manualy unlock drivers door dont use the electric locks. Then put the key in ignition and start it. If that dont work then disconcet positive batery terminal for exactly 10 min. hook it back up and start engine.

Method 1: Press lock or unlock button 4 times in succession. Method 2: Switch ignition ON and OFF. Within 10 seconds press lock and unlock button in succession.
This is the only manual reset
If this does not work go to your local auto electrician
The probable fault could be central locking activator passenger door

turn key all the way on (not to start) let set for 1 hur cycle key and try it.

You need to replace the electric door lock solenoid.The electrical part of the solenoid may be compromised and is not letting the solenoid arm retract or extend to lock/unlock your door.