Normally, passive DC shunts (essentially a big low ohmage resistor) are installed on the negative battery
lead so they will pick up all loads going in and out of the battery
and because they are on the negative side the small gauge sense wires don't have to be fused.
The Mastershunt is different. It is a smart, microprocessor driven current
sensor that sends its current data over Mastervolt's communications
buss. It also has an integrated main fuse to protect the wiring
downstream of it.
It is designed to be the only thing hooked to the positive terminal on your house battery. So wire your solar panel to the load side of the shunt so that the Mastervolt system will totalize all current in and out of the battery.
Be sure to put a fuse near the shunt to protect the solar panel wiring
from fault current from the battery (unless that wire size is appropriate for the Mastershunt's internal fuse).
Or if you have a spare breaker position on your main DC panel you could wire the solar panel output to that breaker (and back feed to the battery through that breaker) and size it according to the wire size.