Interfacing FMG and Northstar unit

[brewski]

I am trying to use my Northstar gps to get MPH to my FMG, and I am having no luck. I have tried hooking the Yamaha white input wire to my violet nmea (+) output, and the black Yamaha wire to the nmea (-) output, with no luck. Any thoughts on how it should be wired, or, are they compatable?

[boats.net]

The white FMG wire connects to GPS NMEA 183 output lead and the black and red FMG wires are not used at all. Set the Gph dip switch in back of gauge to GPS.

[brewski]

When I was out, I cut the black wire off, and still not reading. I have the dip switch changed to read gps, I believe the last 2 are up and down, just the opposite of the way they were when I was getting my MPH from the Yamaha gauge.

I am getting a speed reading to my Furuno radar, so I know the output is there.