Hi,
the problem you will have is the unit must be coded to your vehicle as the software will vary depending on your vehicle spec.
But, to remove the control unit is easy enough. It's just a case of levering out the finishing strip that surrounds it which will reveal 2 screws that hold the unit in place.
Rich.
The light control unit is part of the switch and can be seen in this link which also illustrates how many variants there are......
http://www.realoem.com/bmw/showparts.do?model=ET37&mospid=47720&btnr=61_1060&hg=61&fg=35
You can recode a second hand unit but this will more than likely illuminate the tamper dot on the dash as vehicle mileage is stored in the LCM. The price of coding will vary from location to location as each dealer has its own hourly labour rate, but expect to pay for at least half an hour of labour time.
The switch forms part of the LCM so all comes as one. Ease the surrounding trim away slowly so not to break it. Unfortunately I think the LCM is a dealer only part, but that doesnt mean you have to have it coded at the dealer, you could save money by having it coded at a specialist with the correct diagnostic equipment.
Taking the LCM from another car and coding it to yours will bring on a little red light on the instrument cluster signifying that there is a possibilty that the mileage has been tampered with, i think i mentioned this previously.
BMW Technician
5 years main dealer experience.