MS3 pro no dash tach NA chassis
 

Ok I'm not sure what I'm doing wrong. I directly wired the tach output to the dash cluster but I don't get any tach output besides a quick bounce every once and a while. The MS3P supposedly directly outputs a 12v square wave so I didn't add any pull up or pull down resistors, that's the right thing to do right? What am I missing?

94 is still an odd one that gets the signal from the coils, not the ECU. do the 1K resistor pull up trick.

Wait won't that give me basically a constant 12v signal? 12v from the ECU when it pulses high and basically 12v from the pull-up?

You're thinking the voltage is being sourced through the transistor - which most of the time in automotive it's not. It's almost always switched to ground. Which is why you need the pullup resistor. Without the pullup, there's float voltage and then ground which isn't enough to trigger the tach reading a change.

That's not how black magic works

"4.9 Tach output The tach output supplies a 0 to 12 volt square wave that is compatible with many factory tachometers and nearly all aftermarket units. Just wire its output to the tach signal wire."

​​​​​​That's what the MS3P manual says.

If your coil connectors are (4) pin, you can simply use 2I for that. But if you've wired the tachout directly to the cluster, it should be working.