My 500 had an extra earth cable fitted similar gauge cable to the battery earth connector fitted by a PO (not Bryan as I asked).
I failed to take a photo of where it was fitted on strip down, thinking that's a good idea I'll fit that back there on assembly. The cable is in my spares box, for if & when I remember where it goes.
0.2 Ohms - I have no idea if that's good or bad, I went for plain voltage drop (well lack of) in my ignorance.