The AT&T 6300 is a relabeled Olivetti M24. I just reworked my PSU a while ago. What exactly is your question concerning the wires?
If you refer to the yellow-green ground wires: they are additional grounding wires. Of course the drives are already connected to ground through the normal connector (and the mainboard through the black cable). But Olivetti added extra ground wires - just for good measure and for extra safety. The ground wires are attached to the screw terminals on the right side of the PSU. One ground wire is then attached to the bottom of the main case, just in front of the PSU (you have already attached that, as I see in your photos). The other ground wires are attached to the drives. There is a terminal at the rear of the disk drive (right side) where you can plug the ground wire with the little clamp. The ground wires with the screw terminals are normally attached to the right side of the drives (floppy and harddrive).
