You need to identify the two outgoing nmea feeds from the garmin, that is +ve and ground, and tie them up with the corresponding inputs to the VHF radio.
If yours is like either the Garmin 230 or the 152, blue is the Nmea out and black is the ground - both data and 12volt ground.
My Cobra handbook stated " All Nmea output are red - which they certainly are NOT" so if yours says similar ignore it!
Once you have the hardware wired up, you may need to go to the "advanced NMEA setup" if you need to select one of the special words, which are no standard. Mine however works fine with both the AIS radar and the Cobra on the standard word GPGGA
