How do door locks work on a 1994 Mercedes Benz e420?

The door lock actuators are pneumatically actuated by a pump that is located under the rear deck. Any door that has a key, trunk included, also has a switch built into the actuator that controls the pump.

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When you turn one of the lock cylinders the key turns the actuator for that door closing a contact. The contact turns on the pump and either pressurizes the tubes going to the actuators, or applies a vacuum to move the actuators to the desired position.

Hope this helps.