You would need to talk to Garmin support about the input wiring color code on that unit because I found the manual to have conflicting color codes in the installation manual. I don't want to lead you wrong. There are also many software settings in the Garmin to setup the unit for proper high speed 0183/AIS.
The FA1501 processor of the Furuno FA150 AIS can provide the required AIS data to the garmin via com2, pin 1 (+) and pin 2 (-). I also recommend that the high speed jumper wire be on the port (shorting wire between pin 7 and 8 on the com2).
The FA150 is a commercial IMO regulated unit, so if you need to re-flag the unit or get into the protected settings you must contact your authorized Furuno dealer.