firey

Hi All, I am fitting a Ammeter Shunt between the battery and the starter/alternator so I need cable, however I have measured the diameter which is 11.9mm and I think the amperage is 240 but I am not sure if this is correct as one guy I spoke to told me it should be 315 amps I need so at the moment i'm even Ford themselves cant or won't give me the info . Well I hope someone can help . Oh John if your there give me a clue buddy. I still have the Ford Focus 1.8 TDCi Diesel on an 07 plate .Kindest Regards All...Fred