Garmin GPSMAP 278 pinouts
The connector/pinout information may be applied to the Garmin model GPSMAP 278

 Garmin GPSMAP power and data cable pinout Used by GPSMAP® 276C, GPSMAP® 278,  GPSMAP® 296, GPSMAP® 376C,  GPSMAP® 378,  GPSMAP® 396,  GPSMAP® 478,  GPSMAP® 495,  GPSMAP® 496
Garmin GPSMAP power and data cable pinout Used by GPSMAP® 276C, GPSMAP® 278,  GPSMAP® 296, GPSMAP® 376C,  GPSMAP® 378,  GPSMAP® 396,  GPSMAP® 478,  GPSMAP® 495,  GPSMAP® 496