I want to connect a Raynav 300GPS Plotter with some NMEA equipment...

The Manual for the Plotter says:

"Use a suitable junction box to connect to NMEA equipment"
and
"The NMEA inputs/outputs should be connected to the POWER/NMEA connector at
the rear of the Plotter."

The connector pin functions are deatailed as follows:

Function Color
NMEA data input (+ve) White
NMEA Input (-ve) - common Green
NMEA data out Yellow
NMEA Data Outpout common Brown

There is a connector box in the wiring going to the GPS Plotter. It has a
cable with Red/Black wire pair coming from the 12 volt power supply.

But - here comes the part that totally confuses me - there is another cable
coming in to the connector box which I assume is the (SeaTalk) link to the
Ray Marine equipment onboard
That cable also has a red/black wire pair; The Red is connected to a Yellow
wire and the Black is connected to a Grey wire and this pair is going to the
back of the Raynav 300 GPS.

So where are the White/Green and Brown NMEAwires located???

Do I have to open the Raynav GPS to find these NMEA connectors??? (That
sounds totally wrong to me).

I should add that all the electronics were provisioned in the U.K. by the
boat's previous owner - and I am slowly correcting wiring mistakes made
there (incorrectly sized wires etc.) so perhaps the above wiring is
according to RayMarine specs?

Any comments/help will be appreciated. BTW tried to send an email to
Raymarine technical support - but the webpage was not working correctly - so
that avenue was closed.

Thanks in advance.