Where does this electrical box go?

As of right now my alternator has two fields. Since I have the stock system in place, one of the fields must be grounded. Correct? I grounded one of the fields to the bolt at the fulcrum point that goes into the cylinder head. They should be OK, correct? Or should I go to the body? In the past I have seen it going to the body. I figured the cylinder head would be OK.