Using this link:
SP0000025324 - WDS
By clicking the green connector numbers and following up with the model number of x3 you can find where the connectors are and the connection details but on looking there is not much to trace. The AT output is on the AT chassis under the car - very hard to test. The relay that the AT outputs drive is in the A6009 module (
WDS Wiring Diagram System) and may be faulty but I would think that the fuse F27 driving the reversing lights should blow before the relay gets damaged.
So first up check fuse F27. It only drives the reversing lights.