The rear of the RD4 N1-00 has two main connectors: and B (Brown 12-pin) . Some models have a third blue Fakra connector for GPS or diversity antenna.
Solution: To test an RD4 on a bench, you need a CAN bus simulator (like a simple Arduino with MCP2515) or install it in the original car. siemens vdo rd4 n1-00 wiring diagram
SIEMENS VDO RD4 N1-00 ESSENTIAL PINOUT