Megasquirt 2 Harness Assembly

Let's start with the harnesses.

You'll wanna use these pinouts:


Full size:


Full size:


Full size:

The '95.5-'05 Standalone users require a Tach output circuit.


Please be aware that these ECU pinouts are only correct for USDM cars. There are electrical differences between the USDM cars and JDM and EUDM cars. If you are not sure about the electrical configuration of your car, it is well worth double checking connections with a continuity meter.

The IAC— I/Os on the MS are connected to these DB37 pins:

IAC1A -DB37 pin 25
IAC1B -DB37 pin 27
IAC2A -DB37 pin 29
IAC2B -DB37 pin 31

Just in case you need to know this for a CAS install in an NB or for whatever reason, this is the CAS pinout:
CKP- Pin 24
CMP- Pin 25


You'll build your DB37 connector like this:


You'll build your DB37 connector like this:



There are two options to install the MS:

Option #1

In this option you make yourself a plug-and-play harness to plug the ECU directly into the stock wiring.

The only part you'll need to make your harness is the 64 pin connector. Wire the db37 harness directly to the connector and then just plug it in the factory harness.

  • (1) 64 Pin Male connector (174518-7)

If you have a 90-95 and want to put inputs/outpus in the middle connector you can purchase the 22 pin connector and build yourself a little pigtail connector using the following:

  • (1) 22 Pin Female connector (174515-6)
  • (22) .040" Contacts (175061-1)

all part numbers are tyco / amp, and can be purchased at places like See for more vendors and availability.

TRY for no minimum purchase amount.

Another option is to buy a used ECU from your year of car, which you can disassemble and cut the connector out of. This is possibly the cheapest way of getting the connector you need, as used ECUs are often available through online auctions.


The 3rd option is wiring the DB37 harness directly into the factory harness.

An option here is wiring switch for the igniter and injector paths so you can have either the MS or oem ecu control them at will.

Here is a stand alone wireing diagram from miatamoxie on Thanks!


thanks Joe

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