Or maybe I had the panel lighting on, have to check that before I start to find other reasons...?
The switch when set on GPS makes the plane(s) fallow a GPS route. As for what the High/Low Switch does ? I have no idea.
Might take a bit of the fun out of it, since you'd let the plane fly itself until you get close to your destination, and beggin getting vectors to  land.

Anyway lots of fun. 8-)