Originally Posted by scraph
As for measuring only house battery current ... just connect the shunt to the (-) terminal of the house battery. Connect _nothing_ between the (-) battery terminal and the shunt. The terminal on your shunt that is connected to nothing at this point (the _other_ terminal) can now be considered the (-) battery terminal for this "battery" (which is now a combination of battery and shunt). In this way, you ensure that the current passing through the shunt is exactly the same current passing into the house battery.
So I have a negative bus, then the shunt, then the house battery negative terminal. You are saying that the negative terminal of the start battery should go to that bus and the engine block should go to that bus?