Megasquirt Wiring Schematic (April 2010)...

My old posts are getting more detailed and closer so they will be posted individually. This one includes the MS2 schematic I made when it came time to wiring the unit up. 

MS2 Wiring, April 12th, 2010: "Wiring is a new game for me so I was pretty anxious about wiring up the MS2. I took my time getting comfortable with both the Saturn and Megasquirt schematics before making any cuts (below is a schematic I created). Then I spent some more time sorting out my approach to the wiring. I wanted the outcome to be tidy. Starting with a DIYAutoTune pre-made harness I first separated any wiring destined for the engine bay (in this case the MS2 ground, secondary CTS, and secondary IAT) and pulled them through the firewall grommet attached to the PCM/hood latch cable. Under the dash I separated wiring into direct or splice connections. Before doing any trimming of the DIYAutoTune harness I created a predetermined amount of slack between where I would be soldering and where the harness was connected to the MS2 (in the glovebox). This would give me the slack needed in the event that I ever need to remove/unplug the MS2 from the glovebox and so I could tuck my under dash wiring by reeling in the MS2 harness. Then I did my trimming, leaving a little extra length in the brown wire (Pin 36) for a future Ford EDIS. I had considered de-pinning all of the unused features (IAC, FIdle, etc.) but opted to just cut the wiring a little shorter to hide in the loom. Today I soldered, shrink wrapped, and zip-tied all of my connections with the exception of the wiring that is in the engine bay and got everything tucked up nicely. In other news I also finally installed my SDA dog bones. I originally purchased these unassembled so I could have them color matched to my other black parts. I was disappointed by the sleeves provided for the bushings so I had a friend of mine machine some new ones out of stainless steel."

Saturn to MS2 Schematic

Function : Pin# (PCM/MS2) : Wire Color (PCM) : Wire Color (MS2) : Connection Type
Power        ... A7/28             ... Pink/Black          ... Red                  ... Splice
TPS Input   ... A8/22             ... Dark Blue            ... Blue                  ... Direct
Pin 36        ... C11/36           ... White                  ... Brown               ... Splice (For future reference)
O2 Sensor   ... D9/23            ... White/Black        ... Pink                  ... Direct
Ignition      ... D12/24           ... Purple/White      ... White               ... Splice (Tach Signal)

Injector 4 ... D13/35 ... Light Blue      ... Blue ... Direct
Injector 3 ... D14/34 ... Light Blue      ... Blue ... Direct
Injector 2 ... D15/33 ... Light Green ... Green ... Direct
Injector 1 ... D16/32 ... Light Green ... Green ... Direct

IAT Input ... 20 ... Direct (Secondary Sensor)
CTS Feed ... 21 ... Direct (Secondary Sensor)
Fuel Pump ... 37 ... Bypass MS2, PCM will power

*Splice Connection: Wiring is routed to both the PCM/MS2
*Direct Connection: Wiring bypasses the PCM (goes only to MS2)