Koso Tach inop

Rich Kruger

GT40s Supporter
Was able to start the Beast this weekend for the first time. Yahoo! One issue is the Koso Tach was ions. I have a Chevy performance LS3 that I wired the white tach signal to the Koso with a 12 volt step up utilizing a 5k resistor as instructed. But the difference is that I added a Diode before the stepup in order to not back feed the intelletronix rpm window switch I'm using to control the ac compressor clutch rpm range. So the installation is as such, White gm wire feeding the Intelletronix (which specifically states it should only see negative inputs) then white wire goes through the diode (Band on the diode on the input side) to a joint 12 volt input and 5k resistor union then out of the resistor to the koso. I have an inkling the diode is squashing the tach signal hence no Tach reading. Any thoughts? Please respond in garage 101 not Nobel Prize Electronica jargon;) Thanks
Take out the diode and window switch and check the tach without them in the circuit. If it works, you found the problem. If not, check wiring again. Many people struggle with the idea of the resistor as wired.