In accordance with DIN (Deutsche Institute fur Normung - German standards authority) most wires that are related to the ground will be BROWN or have BROWN color in them, along with another color streak (if that ground is for a specific module), and most power wires will be RED or have a RED color with another color streak (if that is power on ignition, power on LAN, power for whatever...) BMW AG adheres to these standards - therefore, using a miltimeter, check the brown wires to see if they are shorting to the chassis, and then check the wires with red in them to see what kind of power they carry... if you can find a THICK wire, chances are that will be part of the power supply to the module, so you might be looking out for those...