As a follow up to my previous post which discussed how to get your fuel level piped into your MS3, I also needed to get my VSS to work directly (without the gauge cluster being plugged in). I was able to get this mostly setup today (I think I might have some tweaking/testing to do) and wanted to share the details for future miata bros. Donut did a video on this forever ago, but they simply used a GPS based usb adapter plugged into their raspberry pidash. I like have the gear showing and eventually want to use boost buy gear and while technically the GPS based adapter gives you speed, it doesn't give you speed that you can use for the Megasquirt's functions.

Needs:
- MS
- TunerStudio
- Wiring tools, specifically extra wiring, butt connectors, crimpers, deatschworks crimpers (the AXM-120 comes with a deatschworks connector so you'll need at least the crimper tools)
- DIYAutoTune's AXM-120 (there are other's out there, this was just a complete package)
- Options plug for the MS and wiring ends

Explanation
Since the VSS from your Miata is a very high voltage sine wave called a voltage reluctor, and the MS3 can't read this directly, you need a converter to turn this into a relatively low voltage square wave. The stock gauge cluster does this on it's own, which is why your VSS runs directly to it, then to the ECU rather than to the ECU and then the gauge cluster. The AXM-120 module from DIYAutoune fixes this.

Process
Unbox the AXM-120, take special note of each of the pin locations as request. Here's the wiring diagram I made. The yellow wire is on the driver side most gauge cluster plug and the orange wire is on the passenger side most cluster. These are the only pure yellow and pure orange wires. You can also steal 12v and ground from the cluster wires. This just leaves running a single out to the option plug. I used Port L as it was already labeled VSS input on the options plug pin out from DIYAutotune. I was able to test it working while having the car in the air. I still need to get it on the ground to see if the speed of the gauge in the display matches up with real life. If you dont have a gauge that see sthe speed, you may need to go to Advanced Engine -> Gear and Speed sensors, then choose the appropriate options port if you didn't use the default L.



Same as before, let me know if you have any questions.

 

I know I'm updating my own thread here, but has anyone ever done the above and then swapped back to the analog/stock dash? I was going to use the stock dash on the street and the digital for track days but noticed that my speed on the stock dash doesn't work now. It still works just fine in MS3. I checked all of my wiring and nothing seems wrong so I'm very confused. Does the connect to the AXM somehow alter the signal as it gets to the cluster? I have it wired as above where the wiring to the stock gauge essentially just has a wire run from it to the AXM so I would think not, but alas my speedometer does nothing.