ok, so it turned ou the old sony head unit didn't have an ISO connection, but that's cool. It already had the wiring harness for the BMW, so i just snipped off the cables. each wire on the harness was clearly labled, so i just connected each wire to the appropriate one on the pioneer connector.
all installed and working. i'm happy.
still need to test out the player but it's working. i'll have to take pics if you want to see