The radio has only 4 bare wires.
The wiring chart from the radio indicates that the 4 wires are:
1. NMEA in positive
2. NMEA in ground
3. NMEA out positive
4. NMEA out ground
My Garmin's wiring has also has 4 wires.
1. power positive
3. NMEA in
4. NMEA out
So with a multi meter I located the appropriate wires on the Garmin serial connector then on the nifty little DIY serial connector for the radio connector I soldered the NMEA in and out ground wires together to connect to the single Garmin ground.
This seems to at least work in the direction of GPS to Radio. My position shows up on the radio screen and the time of day is also displayed properly.
I just can't confirm if the Radio to GPS will function as I imagine it should. I would expect that if my GPS receives an NMEA signal it will get added to my waypoint list automatically.
I may still just have to call the coast guard on my cell phone, give them my MMSI and see if they will send me a test. I should be able to test the all ships position send as well. Since, there are so few folks with DSC they may welcome a test run.
Thanks for the input.
Portland, Oregon USA