Under the rear seat you will find a bunch of modules on the leftside. The modules you will find are dependent on the options your car has. You can expect to find the zentral karosserie electronics (ZKE) or central body electronics, the OBC relay or alarm module (DWA), the park distance control unit (PDC), the IR-remote locking control unit, the rearseat electrical headrest control unit and the wiper pressure control unit.
The ZKE This system consists of two modules. The relay module (RM) and the generalmodule (RM). The relay module consists of a bunch of relays that control high current systems like the electrical window motores,..etc. This system controls the central locking, the windshield wash and wipe system, the headlight wash system (via headlight cleaning module), the electrical windows and sunroof and the interior lighting. The ZKE also uses a crah sensor also mounted under the rear seat to detect crashes. In case of a crash the ZKE will unlock the doors and turn on the interor lighting.
The inside of my >92 general module. As you can see it only has one PCB. Older types have two PCBs installed. An added bonus of the the >92 control module that came in my 1987 735i is that all four windows have one touch down. Happy happy me :-)
Some E34s come with a "light" version of the RM lacking a couple of relais. So watch out when you replace the module!
Parkdistance control This is the brain of the PDC audible parking aid.
IR-locking system The control module for the IR keyless entry system.
Electrical rear headrests These seem to be standard on all iL models and a very rare option on the shortwheelbase models.
OBC Relais or DWA If your car came without a factory alarm system you will have a OBC relais. This relais powers the OBC. Without it your OBC won't work. Always check this fuse when the OBC is dead and replacing the lights doesn't work.
If you have a factory alarm system the OBC relais' function are replace by the alarm control unit. The OBC's code functions are automatically envoced by the DWA system. There are a couple of different systems: DWA II, DWA III and DWA IV.
The OBC relais. Inside this thing has just a relais.
The DWA II module. This also controls the OBC's power supply
Wiper pressure control The e32 also has a system where the pressure of the wiper on the driver side is increased as the roadspeed increases. This module is called "Anpress druck reglung".
Other modules: On cars with EDC the control unit is located on the rightside near the battery. That should cover all the modules under the backseat.
If you would like to add any comments, remarks and/or corrections to this procedure, feel free to email Mike Oswald and we'll put it on our site. Share your experiences with us so others may benefit from it.