My daughter has an old car 1977, the local (australian) version is a "holden gemini" the australian versions were not fitted with a factory ammeter but some international models were. She has obtained a factory ammeter from another country which fits perfectly in an instrument cluster. The problem is it does not have an internal shunt resistor and of course running the entire current draw thru the little meter would be disasterous. The range of the meter is 50 amps (+ and -) Can anyone suggest a shunt resistor that would come anywhere near being correct? There's no need to be highly accurate, just close enough to be convincing. Looking forward to any help I may get, thanks.