Before you go any further...read this!
Each year BMW has DIFFERENT colors for power. There are 3 wires going to the parking lights. I spoke to the techs at BAVAUTO who told me this. My wires are not the same colors as described by prior posts. Here is the only way to know the function of each wire:
Buy a Low Voltage tester at your local hardware store. It costs about $10 but well worth it.
Take the bulb with recepticle from the parking lamp out of the socket. Put the parking lights on (yes, even though there is no bulb in one of the sockets) and stick your tester in one socket at a time. You should have 3 seperate sockets (holes). By the way, you need to pull out the bulb with the recepticle to see the 3 holes.
With the tester, test each socket. With the parking lights 'ON' test hole 1,2 and 3. Which ever lights up your tester and stays solid, that is your STEADY power. Next, turn on you signals, then place your tester in the next socket (you only have 2 left to test since you already found your power). If your tester blinks on and off, that is your signal line and will not be on until you're using your signals, so don't tap into that one. The last hole, which in BMW's are brown, is likely your ground. You can double check by sticking your tester in the socket. If it doesn't turn on, it is ground.
I did this last night and it works like a charm! This is the most accurate way to find the power, rather than doing it trial by error. Remember ever year Bimmer has a different color coded wiring setup!
Hope this helps.