Garmin G500 Pilot's Manual page 241

1) Select GPS navigation on the HSI.
2) Set the HSI to the desired course (if in OBS mode).
3) Set the optionally installed Autopilot Heading Datum switch to GPSS.
Heading Bug Inactive Indication
4) Engage your autopilot in Heading mode.
NOTE: With GPSS engaged and in Heading mode, the Heading bug will
not control your autopilot heading. This is annunciated next to the HSI by
the GPSS annunciation. The Heading bug may still be used for reference,
but the autopilot will not control the aircraft via the heading bug.
190-01102-02 Rev. B
Figure 5-23 GPSS Emulation Indication
Garmin G500 Pilot's Guide
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