If you find yourself in this situation as I have.  You need to know that Garmin's gWind does not work when plugged into Nexus Wind Data pins 1 & 2 as the nWind is supposed to (with C71 set to on)
Instead, you need to plug the gWind (with the supplied adapter cable) directly to the Nexus network port on the back of the Wind Data display, with C71 OFF, as though it was connected to a Nexus server.

It took me a while to figure this out.  There's no documentation online about it.  And even the Garnin/Nexus very helpful service tech was erroneously looking back at the old Nexus manuals.