Shunts keep confusing people. I think it's mostly the rotten terminology used. They call one side the LOAD side.
It's actually pretty simple. The other side is the BATTERY side, so, connect ONLY the battery to that side.
The LOAD side then goes to the engine
ground, which usually runs thru a bus or a Power Post.
You want and need everything that's going through or from the battery being monitored to go through the shunt, since ammeters are wired in series in circuits, like a flow meter in a pipe.
Battery (& side) >>> shunt >>> ground to engine (load side - bus with all other negative connections)
I call that negative bus my NDP - negative distribution post (I used a Power Post, not a bus bar since I had limited space).