While you are on the phone with Garmin, ask if the GRT HALL EFFECT SENSOR will work with your Garmin system.
You won't have to worry about exposed shunt terminals shorting out or a shunt burning open or degraded starter cranking.
My shunt got fried but was on the Pos not Neg, not sure a battery shunt is allowed on Neg in certified planes. Mine took a hit when I was working on my engine driven feul pump.. the alternator was in the way so I took it out and than the darn positive charging cable kept poking me in the face as I was trying to see where my pump was leaking.. so I did what anyone else would have done shved that dam alternator cable out of the way right to a place I would forget about and grounded it really good against the engine case.. forgot all about it when I was ready to turn the battry on to flip my electric boost pump on to pressure the fuel system and see if the engine fuel pump was still leaking…. BIG BANG when I turned the master on.. took out both 70amp alternator breakers and the next component inline the battery shunt melted.. took a few days of troubleshooting to figure that out.. the low power items would work but the high items dead.. and the battry ammeter was slammed to the discharge side.. will let that sit for a couple days and see if some sharp person here can explain why those things were happening with the shunt burned apart.