The BCM is Body Control Module - it runs the wipers, turn signals, and handles a lot of communications between SKREEM and CLP/SSM and also processes switch inputs from the console switches and passes this information to the various modules in the car. The BCM plays a role in some, but not all, CAN BUS signalling. The BCM tells the top module if the retainer latch switch is open or closed, and if the windows are going down properly..

The BCM is in the middle of a LOT of what is going on with the car....