I have a GTX327, and it has a squat switch which is used to switch from
ground to air modes. Maybe your 330 has the same. You may not need the GPS
connected to the 330... I am no expert, I am reading this out of the manual.

By the way, I am interested in making a remote switch for entering
transponder codes. Any info you have on the data protocol in/out of the 330
would be of interest. There are other garmin products that can "tell" the
327 what code to enter, but Garmin is coy with the data protocols.

Bill