I/K Bus Topology
The I/K bus consists of a single copper wire. The wire color of the I and K bus is uniform throughout the vehicle with: I-bus WS/GR/GE and the K-bus WS/RT/GE (Note: 2001 E39s with base Kombi have changed K-bus wire color to the same as the I-bus, WS/GR/GE).
Due to the linear structure of the network, the I/K bus is available for other modules in the event of a disconnected or failed control unit. Just as the CAN bus, this is referred to as a "Tree" structure with each control unit occupying a branch. The I/K-bus provides the diagnostic connection to the control units located on those busses (except IKE/KOMBI).
Always refer to the ETM to determine the exact wiring configuration and color for a specific model.