The larger circle on the right of the picture is a "weight plate" that is exactly the same as the orange/yellow circles you see on some tanks and other equipment. It is used by engineers to allow safe travel of vehicles over bridges, on ships, or on ferries. They are changeable on the CUCV in particular because the weight can change quite a bit for a smaller vehicle considering some of the more light-weight bridges it "could" cross.
The other piece, IIRC, is a jumper port for when the batteries have gone dead.