The shunt is energized but has nothing on the load side, and on the battery side the fuse was removed so it is not connected to the battery neg. Is there a fuse holder still there?
So the only wires on the shunt are the amps measuring wires on either side of the shunt? and the monitor has positive 12v?
It is unusual that there would be a fuse between the shunt's battery end and the battery neg post.
I have not figured this out--just collecting info now. ISTR you had a similar problem way back with the battery switch on the neg side, now gone? Is something connecting via the metal battery box?