I have the same issue. And receiving conflicting information from Garmin customer support, doesn't help.
Installed a Simrad HS60 GPS compass with a Garmin GMI20 display, after Garmin support said I could use this to provide heading to the autopilot and radar
. The HS60 was initially seen by my Garmin units, except for the autopilot would not use it as source. (Garmin software from around September 2017).
Then I updated to the Garmin software dated February 2018, and all kind of issues came:
The Garmin units (chartplotter, autopilot..) no longer recognized the Simrad compass. Everything is connected via NMEA2000.
Had to replace the GMI20 with a Simrad display, before the Garmin units again recognized the Simrad compass.
Garmin support claims I was not able to get any information from the Simrad compass into Garmin units, prior to the February software update, which according to Garmin, added support for external sources.
Totally opposite of my experience!
Garmin support also claims that the issue most likely is because of other electrical
units powers on/off, and thereby causing problems for the NMEA2000 network. This has been checked and is not the issue.
But: Garmin has eventually achnowledged that the autopilot will NOT take heading information from any other sources than Garmin only, even with the latest software.
This feature will "maybe" be introduced in future software updates - again according to info from Garmin support.
The Garmin reactor heading sensor is very unstable, and a calibration is often required, in addition to a "set North" after every major change in heading. (Say more than about 20 degree change).
After updating to the February 2018 software, the heading sensor is living its own life, and differences between heading and COG changes every few seconds, with the all time high record
of 160 degrees difference!
This can introduce interesting effects, especially if using radar
Have sent the heading sensor back to Garmin for repair and/or replace. (Just like I had to do a year ago, after I had a Garmin service
person onboard to check my systems...) Hopefully things work
a little better this time.
So far, I am absolutely not happy with the conflicting information from Garmin customer service