Hello:
The bare wire is the shield drain wire. It should only be terminated at one end. Which end is the trick. the convention is that the shield is connected at the source only. In the case of a depth transducer, for instance, the shield is terminated at the transducer, and not connected at the instrument end.
Connecting both ends creates a ground loop and makes the signal very noisy - the shield essentially acts like an antenna and picks up all the noise in the boat. I would be very suspect of connecting your shield wire to a ground of a VHF or anything else - this is a ground loop waiting to happen.
On some Navman / Northstar instruments (the depth 3100) there is no black wire, and they expect you to use the bare shield wire as the negative or ground. Not a good design.
I would try wiring everything but leave the bare wire unconnected first; if everything works, then leave it unconnected.
NavBus NMEA standard wiring is yellow and white wires, unless wiring to a Repeat 3100, which uses yellow, white, and green as NMEA.
This:
http://www.navmanmarine.net/upload/M...us_eng_web.pdf has a schematic of the NavBus junction box, which details all the connections and wire colors that Northstar and Navman use.
Best Regards,
e
.::.