Courtesty of Mojo from Acurazinc.com
http://www.chrishorne.com/gallery/SNHOND3
Purchase the audio harness for the Accord (P/N 08A31-0E1-010) from any Honda place; it's around $30. Split open the outer jacket of the SNHOND3 cable to expose the wires. Specifically, we need the brown, blue, and orange wires in the SNHOND3 cable. Cut the female end of the Accord adapter off, and cut back the outer covering. There's a couple of grey shielded cables inside of this one- one has a grey and orange wire, as well as the metal shielding. Cut back all other wires, and expose the grey and orange wires, and twist the shielding into a wire. Next splice (either by cutting the SNHOND3 cable's brown, blue, and orange wires, or exposing the wires and soldering in, or by using an inline crimp; I cut and soldered for a cleaner installation) the lines together like so:
Accord grey -> SNHOND3 brown
Accord orange -> SNHOND3 blue
Accord metal shielding -> SNHOND3 orange
Note that the SNHOND3 cables are straight through-you're just Y-ing off the three wires to the female connector.
Once all of this is done, seal with electrical tape or heat-shrink. You'll end up with a cable like the last cable pictured (see link). Unplug the white connector under the Navi (when the CD changer tray is removed), plug it into the female connector. Then plug the SNHOND3 cable into the Navi and into the interface.
Hope this helps.
-Jimmy