MS2 Tach In Confusion
 

I'm having a hard time getting a proper tach signal on my ms2. It was built using Frank Westfield's writeup (which as recently been pulled, although I was able to grab the text from google's cache).

Currently my primary tach in is wired to pin 4F camshaft SGT and the secondary is wired to pin 4G camshaft SGC on my '96 miata as per another wiring diagram that I found. I'm a little confused if they should be wired to the crank angle sensor or the cam angle sensor. They're both commonly referred to as CAS, and I've seen instructions for using both. In Frank's build, it says that the crank goes to pin 24 and the cam goes to pin 25 (I built a second opto circuit instead of the simple pullup). I just don't know if I want SGT or SGC or CMP or CKP, or which crank pins on the ECU are which.

Right now my RPM bounces between 0 and around 150, So I have a feeling that I'm not using the correct input...

Got it figured out. I was connected to the correct pins, I didn't realize the second sensor was just for OBDII and didn't come on earlier NA8's. The bouncing was just noise, I replaced the wires with shielded ones and the car started right up.

huh? there's a cmp and cmk signal on all miatas from 90-13