Hello Nick,
From the FCV585 power/data cable, you would want to use two wires to receive NMEA0183 data. Yellow is receive positive and green is receiving negative. From the ICOM M506, take the two wires (white is out positive, and brown is out negative BUT confirm with ICOM on their wiring) to our yellow and green. So white to our yellow and brown to our green.
After making the connection, turn on the FCV585, then select Menu, scroll down to NMEA, make sure the NMEA0183 version are set the same on both FCV585 and ICOM, NMEA Port is set to IN/OUT, and you can select Port Monitor to check if there’s data coming in from the ICOM. It's a great test screen to confirm.
YachtyBoy