For use only on 66 models. Will not work on factory 65 GT/Pony Interior cars. The ammeters on these cars are different from a 66. If you wish to convert to 66 style round gauges, this gauge will work as long as all 66 wiring is utilized. If you have any questions, contact us for a picture of the back of a FACTORY 65 GT/Pony Interior ammeter.