Got new Isspro tach today, installed just as paperwork said, and it won't work. Even replaced crank sensor thinking that may be it. Put volt meter on signal line at the tach, on MV scale, started engine, got a reading and it climbed as engine speed increased. Does any one know what the voltage readings should be at idle and want scale to use. I;m thinking it's just a bad tach out of the box. Isspro did say to return it and they would check it