MS1 V3 Pinout for Tacho
 

Hi folks, just completed the assembly of my MS1 V3 for my MX5 MK1 1.8 1997 UK Spec, I have installed the fan and ignition mods as per the excellent "super important megasquirt threads "write up on here.
I built the MS1 V3 using the megamanual instructions..

I have a question about the Tacho output pin number coming off the megasquirt.....

I am making a stand alone harness for a 96/97 1.8 model but I do not know what pin # the megasquirt uses for the Tacho.

At the moment pins 20 to 37 are all being used for other things so I can not see what pin from the megasquirt connects to pin 4l on my cars connector, to get my Tacho working....

Any help with this would be great..

There isn't a dedicated pin on the MS for driving the tach. You need to build a circuit inside the MS to create the tach signal, and then connect the output of this circuit to any available pin on the DB-37.

Use the first illustration in the above link. The "selected pin on the PCB" can be JS0, JS1, JS2, JS3 (or a couple of others) depending on what's not already in use elsewhere. You will then configure the "Techo Output Pin" (under "More Settings") in TunerStudio / Megatune to tell the MS to use that pin to generate the tach signal.