Connecting VHF and GPS
Connect the GPS128’s blue wire to the Icom’s central core. Connect the Icom’s outer core to the Garmin’s ground (black wire). You’ll need to check that the Garmin is set up to output NMEA (look at the Interface page and set it for either NMEA/NMEA or None/NMEA.
Need to check this is set to outpu NMEA, by default it is set to Garmin