I have a B&G Chartplotter, a Zeus III. As soon as the NMEA power is turned on the Chart Plotter and all the instruments come on.
I had looked at how I could stop this default behaviour, so that I could have the wind instruments, for instance, turned on without the power drain of the full Chartplotter.
But I have discovered, and I think this should work for most Navico Chartplotters, is if you push the power button three times it not only puts the Chartplotter into Dim mode, almost turning off the display but it ALSO puts all the NMEA powered Titan displays etc. into dim mode saving even more power.