If you do have a ground, wire it to the load side of the shunt. In some applications the ground/chassis connection carries current, and needs to run through the shunt to keep the meter accurate.
You do not generally need to bond the ground/chassis to negative, especially if you don't have an inverter.
The wire is not necessary.
I do it becsue I've seen allot of crazy things and I never know what will be done in the future.
these two quotes seem to answer my vehicle chassis ground question.