The interesting wires for data transfers NMEA are yellow one (NMEA OUT), green one (NMEA IN) and blue one (GND). The yellow wire will be used to send the GPS data in GPSNavX or MacENC, green wire to transfer data (waypoints, routes) Mac to the GPS. We'll have to weld these three son on the corresponding pins of a serial DB9 female (all retailers of computer), and then use a cable Serial / USB to connect to your Mac, the Keyspan item below is strongly recommended. I do not recommend you run yourself in making a USB plug.
To connect multiple NMEA devices on a single USB connector, I refer you to the detailed explanations available on the page Hardware Onboard from my website, mostly to the chapter dealing with the multiplexer.
If you send your data only to the Mac, Just set DATA2 (RS232) on REM (Remote) and NMEA VER (Version) on 1.5 or 2.0.
If you send data to your Mac and also to an autopilot, must now set DATA1 on AP (AutoPilot) and DATA2 on REM.
For the meaning of NMEA sentences, You can view this useful document PDF.
Settings in GPSNavX or MacENC
The GPS must be connected to the Mac and turned on before running GPSNavX or MacENC. In the drawer " Settings "GPS panel, must set the type to "Other", port to "keyserial.xxxx" and speed " 4800 ". To transfer data to the GPS, Both applications use the NMEA sentence $GPWPL to send waypoints when you activate " Transfer > Export to GPS… "Menus Waypoints or Routes. From experience, if the type "Furuno" is used in the parameters, transfer replaces all existing waypoints.
And of course you have not forgotten, before all, installing Driver Srie / USB you downloaded on my website (the bottom of the page).