I was looking at the wiring diagram for my 02 x type and the way I se it, the left rear door speaker wires pass through connection CA25. I read that this connection is near the left B/C post. Anyone know what or where the left B/C post is? That 14 pin connection seems to be a good spot to tie in the wires for a subwoofer.

 

C25 is going to be found mid-way up the left side "B" post. You can easily see the connecting point if you open the left rear passenger door and look for the harness as it passes from the B post to the door. See photo below of door-side wiring harness and connector.