Could anyone advise me of the correct wiring for conecting a garmin gpsmap750s to an AIS 600 I have both looms and both manuals but they appear to conflict.
I would connect these using an NMEA 2000 bus as per page 3 in the AIS 600 instruction manual here.
That should mean that there should be no problem matching anything other than just ensuring your NMEA 2000 network is setup and terminated correctly as per Garmin's guidance.
This may mean you'll have to build an NMEA 2000 network if you don't have one already (guidance from garmin on building an NMEA 2000 network can be found here), otherwise you can add each device to your existing network by using additional network T pieces and drop cables which show they are included with the AIS 600 and I haven't checked but would think they'd also be included with the 750 plotter also.