How do you use the GPS switch to run a track line in the Piper Cheyenne. Nothing happens when I click the switch. I think I remember the radio has to be tuned to a certain freq, but I'm not sure.

From memory, the Aerosoft Cheyenne by Digital Aviation uses the old Trimble GPS. That requires reading the manual, as it is not the same as the default FS9 GPS. There is a tutorial document somewhere in the Digital Aviation folder.

It won't switch to GPS flightplan track unless you have Nav1 set to a NON-ILS freq. I usually load the ILS into Nav1 standby and something obviously not ILS (like 108.00) into active. To transition from GPS to ILS, I set AP HDG mode to make the turn to intercept ILS GS (or just hand fly it), then swap Nav1 freqs. Once I verify the ILS is active, then AP NAV mode to capture it.