No wonder I'm having trouble getting this sorted out. From
http://www.bmea.org/wp-content/uploa...nmea-guide.pdf
"There are only two wires involved - how difficult can it be? Well, although you can’t do any damage if you get the wires the wrong way round, the major problem with NMEA interconnection is that there is no set reference standard with regarding to NMEA connections - the two wires can be any colour and the terminals can be called anything - NMEA Data and Common, NMEA + and -, NMEA A and B and so on. Some manufacturers don’t have a dedicated Common terminal, in which case you have to connect the common wire from the other unit to the battery negative of the equipment you’re interfacing with."
and
"Reading the various user manuals you will then find that there is little consistency when it comes to references for the NMEA connections - some talk about NMEA Data and Common, others NMEA + and - or even NMEA A and B. Whatever they call them you basically have a wire that supplies data, plus a return wire. Don’t be distracted by the wire colours of any cable that might come with the
unit - there is no colour standard for NMEA cables and it will vary depending on the manufacturer and which cable they are using.".
I have emailed Northstar tech support.