I just replaced my orig Stewart Warner Tach with a new Gaffrig GL6000W. I think that the rpm's shown are not the same as my old tach, off about 600 rpm. When I installed the tach I reviewed the factory settings, which from the instructions seemed to be set for 8cyl.
I want to recheck these switch positions, does anyone know what they should be for a 420 merc ? I was cleaning up and threw out the instructions.