I just changed mine for a "brake light circuit" error that I kept getting...it was a four-pronged.
I also remember seing another switch up under there that looked the same...farther up though...maybe that is the 2 pronged one?
<img src='http://www.bmw-forums.com/forum/uploads/post-46-1094081870.jpg' border='0' alt='user posted image' />
Clear Corners and Sidemarkers
ZKW Euro Ellipsoids w/ DDE Enhanced
Debaffled Airbox w/Green Drop-In High Performance Air Filter