I just recently brought up the same question in a topic called "Copnnecting
Icom M502 to serial GPS unit" look me up under that thread.

"Jon Gauthier" wrote in message
...
Another question - and I know this has been hashed before but a search
didn't turn up the answer:

In a network with NMEA equipment from different manufacturers in which
some equipment has a real, separate NMEA (-) lead and other equipment
that takes the cheap route and uses DC ground for the signal return, is
it best to just leave the NMEA (-) leads floating, or run them to DC
ground?

I do have a DC ground bus bar for all my nav equipment (including VHF
but no SSB) that ties back to the main DC ground bus using a #6AWG
cable. According to my stereo's AM band, the system seems electrically
quiet