On a 72, rear defrost is black. Of course 74 is probably different. It's also the only wire of about 12 awg size that goes to the rear of the car.
I dunno what your mystery connector is, but I can tell you green/white will be a ignition hot wire to power something. Solid green is upstream of a fuse, and green/white is downstream of a fuse. Brown is always the negative side of a circuit, but brown with an additional color is usually a ground that is contingent on something, for instance the door switch has a spotted brown wire to it because it becomes a ground when the switch closes.