Where the parallel connection is made is dependent on the year of the car.
It's either in the door sills or at the underseat speaker connector.
This is described in detail at the Alpine installation PDF at the end of
the links.
base system wiring pre/post 3/09
https://www.google.com/url?sa=t&rct=...tDpLJPcGkw_ui_
Base System Guide
http://www.e90post.com/forums/attach...5&d=1493273253