I have a Smartshunt ready to install as a DC energy meter on my boats domestic alternator, but this has the negative via the grounded case and engine. I also have a separate engine battery and alternator but they share the common negative return via the engine. This will add to the existing BMV702 on the domestic batteries. I have seen many comments that in this case, you need to have a shunt in the positive cable.
Thinking about this, I believe that I can wire it up in the negative cabling per the attached sketch. The negative return from both alternators splits at the new Smartshunt to separate out the current from the two alternators so it will only measure the domestic alternator. In the existing wiring, the alternator negative, the ground and the engine battery -ve all connect to the -ve bus and this works OK with the BMV. The boat is steel hulled and it is not used for any negative returns, everything is fully wired to the -ve buses.
The sketch ignores fusing, isolation switches, minor wiring to the shunts.
Am I missing something in my wiring layout.