I did not need an electric brake controller in my towing application. I spent more money on the wiring harness from BMW than I did on the hardware. The factory harness installs very easily and worked perfect. If I remember correctly, there were more than 4 wires going out to the recepticle, those extra wires might have something to do with electric brakes. Judging by my past experiences with towing and trailers, this BMW (X3) might not be up to the task of towing anything that would require electric brakes.