I have a 40hp Evinrude CE40TLESR S/N C2465925 in an 18' Crestliner, there is no tach installed. I do have a Fluke DMM with a Htz pick up, can I take the input from the grey wire at the ignition and divide the result by 4 (stator output) to get my RPMs?<br />I know I should just get a tach but I...