the third wire attatched to your RCA leads is the remote wire, on the back of your head unit their should be a wire you can hook it up to if their is no wire i spliced mine into myignition on wire on the head unit, earthing the amp should be quite simple pull up the carpets in the boot and see if you can see an earth near the rear lights, you obviously need a fused power wire running from your battery to the amp and the speaker wires to hook it up to your speakers/sub.

hope this helps