Webasto has different remotes/receivers to control the aux heater.
My X5 3.0d is equipped with the T70 remote which just sends a signal to the (T70) receiver (no feedback).
The T80 remote will do the same but also gets a signal back from the (T80) receiver in the car indicating that the aux heater is working.
Now they came out with the T100HTM (www.wohlfuehlklima.de/v_products/t100_en.php).
The receiver is located next to the car battery below the spare wheel in a plastic frame containing several modules.
Mine has 2 connectors, 1 for the antenna and 1 with 3 wires.