BMW Rear View Camera Noise Filter, Voltage Rectifier When connecting an external backup camera, it will not function correctly in a BMW. This is because BMW converts the voltage and pulse signals when trying to draw power from the reverse lights. Even with a relay in between, the relay will not operate, so this product is necessary. Simply insert it between the camera and the reverse power supply. If you don't understand how to wire it based on the photos, please refrain from purchasing.