G3X - INS-429 integration

I think I know what's wrong, but if anyone knows for sure, confirmation would be nice.

So this journey started when I read this in the G3X installation manual.

"VOR, localizer, and glideslope information from a Garmin GNC 255 or SL30 VHF NAV receiver is also supported. These radios connect to the G3X system via an RS-232 connection to a GDU display"

So I read the INS installation manual, the SL30 manual. Because the INS 429 and the SL30 support the same NMEA sentences, I had hoped the INS would couple with G3X. So I hooked up the serial out (omitting serial in) from the INS 429 to Serial In 3 in my GDU 375. I should note, I already have a GTR 200 and it happens to be connected to serial 3 out on the same GDU head.

When I boot up and fly, I am able to see a disabled "CDI SRC" [thumbs up].. It's a start. It it never enables. So I think here's what's wrong...

These NAV inbound NMEA sentences are key...


Request periodic output of CDI, GSI, and related flags at low (1Hz) rate.


So... I think because I didn't do the opposite direction, this inbound command can't tell it to do the outbound commands.

Has anyone tried doing this? Will it work or should I just stop.

Thanks!