Brown/purple wire is the ground for the door switches - when you open the door and the lights turn on, that is the wire that grounds the lights so they can come on.
The stock tweeter wiring is gray/green and green/yellow to the C404 (passenger) and C405 (driver) connectors. Those are the big, rubber encased plugs where the door wiring goes. From there, gray/green stays that color to the woofer, and green/yellow stays the same to the C406 (passenger) and C407 (driver) connectors. Those are single-wire connectors located somewhere around the woofers. Passenger side then becomes 2 gray/brown wires (out of that single-wire connector), driver side becomes two gray/violet wires out of that single-wire connector.
EDIT: In fact, you can see the passenger side stock tweeter wires exiting that plug in the picture I took. The side of the connector facing you, at the top edge.