SATA Port 2 is already taken!

Hi,

I'm in the middle of trying to use your guide to install a secondary SSD drive in my 2011 iMac. When I got to Step 33 where it talks about putting the supplied SATA cable into the Port 2 slot, there is already a cable in there, one that looks to be connected to my current hard drive. The cable that is in Port 1 is the other side of the optical drive plug I took off earlier. The optical plug is not the right size for the socket, in fact, it looks like it fits the slot marked SATA 0. What does this mean? Did someone miswire my computer or was this intentional?

As nothing like this is mentioned in the directions, I didn't want to move anything just yet before asking to see if this was at least normal or not. Any help would greatly appreciated.

Thanks,

Carmen