Thanks Johnny. I have wired it all up and it seems to be working.
I do not have a "backbone".
With one sensor (Airmar Weather Station) and one Screen (FI501) on the NMEA 200 I didn't think I needed it.
I understand that if I ever want to expand the system (as it was designed to do) I would need to set it up properly with a "backbone".
Don't know how to attach a diagram so here is how I wired it:
12VDC goes into the (rear view) right side of FI501.
The other socket on the left rear side of FI501 is fitted with a N2K lead (supplied with the splitter box) this is a pigtail and goes to the splitter box.
Splitter box manual is here
https://www.airmar.com/uploads/InstallG ... 494-02.pdf
I can't see why both outputs won't work concurrently but I have emailed Airmar to check.
There is no power going into the splitter box.
The NMEA 0183 output from the Splitter box (I only used the transmit wires) go to a
YakMUX 3 Port NMEA 0183 Multiplexer/Combiner
This also picks up data from a Navnet VX2 and supplies a Simrad IS15 Multi screen so I get Depth or SOG or Wind on a screen I can see from anywhere in the cabin.