looking at whats available back emf etc

I have a classic car that in my stupidity i leave the lights on quite often. As a result i want to build myself a "lights on warning" im thinking of having some form of switch either electronic or software that knows when the engine is running by the voltage on the coil problem is there may be slight emf issues with the coil and as it is ballasted the voltage

I guess what i am trying to ask is is there a way of shielding the arduino from any emf and is it sensitive to varying voltages on its input. the voltages could vary from around 6v to 9v