I've done this with the Prodigy and basically the same install instructions. I mounted my controller just above the dead pedal on the left hand side of the drivers side. Towed our boat for 2 seasons using this and it works perfectly. With the prodigy I can disconnect it from the wiring simply and remove it when not in use.

The articles mentioned above are great documentation and just give yourself an afternoon to do the install.

It's nutty that BMW hasn't addressed the brake controller issue. The big 3 have done this for years and Toyota too with the Tundra and they make it so easy to install a brake controller. Hello! BMW are you listening?

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2007 328i Sport, Monaco Blue
2011 X35D - sold -Space Grey
2004 X5 4.4i - sold - Kalahari Beige
2001 X5 3.0i - sold - Pearl Beige
2006 325i Sport, Sonora Beige
2000 323i - sold - Sienna Red