I have a 2002 C320... thought the drivers side seat control switch was bad. Replaced it, no luck. Apparently there is a door control module, and seat control module as well. Since the seat, and steering wheel do not work am I looking at a door control or seat control module replace??

 

door control module is in the door, usually attached to the door itself. and the seat control module is under the seat. Its very hard to say, could be something more complex. check all fuses first and check connections under the seat.