I have just completed extracting from an MGTF engine loom exactly what you are looking at to retrofit to my MGF. There is a brown wire going to the starter (ring connector)- the other end goes to the 80 amp fuse held in a translucent box (left side of your picture), the other end of which goes to the alternator in the form of a square connector, which I believe is what you are asking about (all wires are brown and very thick). Basically, a brown cable connecting starter and alternator via the 80 amp fuse,