I have a 2004 Elektra Glide CVO and am trying to replace the original radio with a JVC aftermarket. I'm confused about the two harnesses on the back of the old radio. The new one has only one to use. Which one do I plug into? (one harness is black. the other one is gray). I'm trying to use a Scosche HD7000B harness and a PAC SWI-RC interface.