One other tidbit of behavior I baked in that’s different for CalTopo mode vs NMEA is that instead of forwarding a newly received position as a WPL, it traverses all of the nodes in the NodeDB with valid positions and generates WPLs for them on a 10 second interval. I found this to be better for team tracking.
Noob here, pardon my ignorance. I did this with APRS Ham unit a year back and now want to give this a go.
You mention that the Garmin wants 12v. Is that in the serial, or just to power the device?
What do you recommend for converting the uart to serial? The max3232 isn’t handling that, is it?
My goal is to see the location of other T-Echos on my network on the GPS(Montana750).
Your example isn’t a TEcho but perhaps you know… Is the serial out of the TEcho that device’s location or the received packet’s?
Also, on the TEcho, is the serial coming out the usb-c or the pins
Thanks!
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No worries, I also come from the world of APRS. 
The 12V is the voltage on the serial for the Garmin device (regular serial uses +/-12V vs 3.3V ttl)
As stated in my initial post the MAX3232 handles the 3V3 to 12V conversion (It has pump circuit for the 12V signal, VCC is 3V3)
Regarding the T-Echo I haven’t tried it, but I suggest reading the schematics for the T-echo and perhaps check with the devs on Discord whether the T-Echo has any serial output that’s usable for this or not. I don’t believe so but perhaps I’ve missed something.