I have a start button wired up in my car right now... the only thing you have to do for that is wire the button between the green ignition wire and the starter relay under the dash (if you get the Z8 button, there's a safety feature in the button... you have a 3rd wire to tap into the hand brake switch which allows the button to engage the starter only when the hand brake is engaged) I'll snap a few pics to show the more simple of the 2 installs (the E90 PSS button install is a little more involved, but not by much)