The reason you can't match it up to AWG is because it isn't AWG. It is spec'd in square millimeters of cross section. The wiring diagram manual lists the cross-section of all the wiring, it seems, except for the alternator ground. For instance, the wire from the alternator to the starter is 6.0mm squared. The key (lower right on the map) shows un-marked wiring is default 0.75mm sq. The numbers get pretty small and hard to read in the Bentley copy.

Although 6.0mm sq. is closest to AWG 8, I would use 10 gauge for the ground, but what is more important is strand count and insulation flexibility. For a very short wire, ampacity rules can be derated, but to survive the flexing between two moving parts, flexibility cannot.
--
Art Benstein near Baltimore

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