After a few months of asking on a various forums, no one seemed to have an answer to getting an aftermarket tachometer to work on a 2010 EFI America. However after trawling Google, found a set of instructions for a tach adapter that explained if the tach wasn't working as it should after wiring in the adaptor, to couple a 10000 ohm resistor and a 0.1 microfarad capacitor in parallel between the tach imput wire and earth (ground)..... And it works, now showing proper RPM.
