Sorry to revive this, but I ran into a hurdle when attempting to read my ECU in my 2006 WRX. There are green connectors on both the driver's and passenger sides of the car. The driver's side is a larger connector and doesn't require taking any plastic fasteners out, while the passenger side usually needs you to remove a couple fasteners to get to the connectors.
I was trying to get ECUflash to read my ECU but I kept wondering why my WRX didn't seem to be going into "test" mode. Then I found this site talking about driver's side so figured I'd take a look under there and sure enough found the 2nd larger green connection. The iwsti.com site talks about 2006 STI and connecting the passenger side but not the driver's side, so I posted there on a thread that was dead since 2009. This thread is even deader....sorry for that, but I hope to help some other newbie that just bought a 2005-2007 WRX and wants to mod it.