One problem related to wiring has been reported for the 2004 BMW X3. The most recently reported issues are listed below.
Driving on freeway and driver's side seat heater overheated burning seat and creating abundant smoke inside car's cabin. This was a very dangerous situation on the freeway and I have no doubt that the seat would have caught fire if I hadn't felt the burning sensation early enough. Dealer stated that they had never heard of this happening and quoted $1200+ repair. Researched online and found many similar occurrences. Decided not to repair and chance the same happening again. Disconnected wiring to seat heater.