Parallel Harness help!
 

Im attempting to build a harness and i have a few questions. First, there's a bunch of wires coming from the MS harness that i have no idea where they go. Here are all the wires that i have left over, a gray wire that says TPS(dont see it on the chart), a blank yellow and blue wire, purple Fuel pump (i think its for the 1.6) and 4 IAC wires which i believe i have to use 1 for my boost controller.

Second question, do I just "splice" the MS harness into the existing wires while still keeping them connected to the stock ECU?

PS. Does anyone have a single (1) 26 Pin Female connector (174516-6) and pins that they might sell to me?

BTW, i have a 1994.

What diagram were you following when you soldered all these mystery wires into the DB-37?
It goes to the vehicle's TPS wire.
Don't recall seeing this in DIY's standard wire package. Need to know which pin it goes to.
Actually, the 1.6 can't use that wire. It's for the 1.8, but if your stock ECU and MAF are installed, the ECU will take care of it.
Again, depends on how you wired the DB37.

Some you splice, some you cut.

Fuel, spark, and anything else you want the MS to have control over, you cut. CAS(x2), CLT, and anything else you want to share with the stock ECU (sensor inputs, basically) you splice.
Good year. :D

Since i bought it used, i assumed that that the harness was prebuilt by diyautotune, its not.
The blank yellow and blue are in pins 2 and 3. Im guessing that i will using those for my basic installation.
I still do not understand the TPS wires. I have 2, a blue and a gray. The blue reads TPS SIG and i see where it goes on the diagram, but the gray one says TPS VREF.

Thanks for the help!

Joe, I thought the 1.6 uses the purple wire for the fuel pump?

From the FAQ:
"Fuel Pump:

FUEL PUMP 1.6L only:

It's the purple wire (FP). Tap it into the light green wire off this harness under the dash:"

http://www.boostedmiata.com/MS/fuel_pump_lead.gif

Oh- two wires, one yellow, one blue. I read that as a single yellow/blue wire.

Ok, al the answers are in the MS schematic, which is here: http://www.megamanual.com/ms2/megasquirt_ShemV3.00.pdf You really do need to become familiar with it, rather than just blindly poking around and following write-ups, especially since this MS is used, was assembled by someone else, and has mystery wires hanging out of it.

Pins 1 and 2 are both grounds. Pin 3 goes to the SPR1 pad internally, and the function of this depends entirely on what circuit or mod the builder connected to this pin.

Again, schematics and documentation...
TPS SIG (pin 22) is the 0-5v analog input for the TPS signal. TPS Vref is a 5 volt output for you to power the TPS with- TPSs require power and ground to operate, as they're basically voltage dividers.

If this is a parallel install, you don't need Vref, as the stock ECU will still be powering the TPS.

Ok, yeah- if you run a wire across the dash and tap the COR as you've pictured, then yes. There's no wire on the stock ECU harness that accepts a closure to ground to drive the fuel pump, as it wasn't originally done by the stock ECU.

On the 1.8 cars, the ECU did control the fuel pump, so there's a wire on the ECU harness you can use for this function without having to tap any relays. So long story short, the violet FP wire gets used on both 1.6 and 1.8 cars.

But you're correct- the mod you've pictured is 1.6 specific and gets the fuel pump working in absentia the AFM.

Ok, now im scared. I thought i had all this pretty much figured out, i guess im not. I have an IAT kit that i will be installing, do i still need to connect the FP wire?

Since this is a parallel install, no. (This is what I hate about parallel installs- all the "you hook up this, but no that" bullshit)

You need to connect the following:

1- Power (switched, from white/red wire)
2- Ground (lots of it)
3- CMP and CKP inputs (internal pullup not required)
4- CLT (essential that internal pullup removed)
5- IAT (with pullup)
6- TPS (optional, and single wire only, Vref not needed)
7- Spark
8- Fuel

That's it. No FP, no IAC, none of the factory O2 sensors or emissions shit. Just the stuff on that list.

Thats great info, but can you clear some things up for me? What exactly is the CMP and CKP? What do you mean by "pullup?"

Also, i have a LC-1 that i will be hooking up to the MS. I just connect the yellow wire to the MS and completely disconnect the o2 wire going to the stock ECU?

CMP = Camshaft Position sensor
CKP = Cranksheft Position sensor.

On the NA, they're both housed in the CAS on the back of the head. In the NB, they're seperate sensors. But both provide essentially the same info- the CKP gives you a pulse ~70 degrees prior to each TDC, and the CMP gives you a pulse every other TDC, to identify which CKP pulse is which.

Uhm... yeah. Wow. Ok, Abe, could you step in here with a picture? I don't have PaintShop installed on my little laptop.

In short, a pullup is when you tie an input to V+ through a resistor, with the expectation that whatever sensor is connected to that input will provide a closure to ground when "active", thus pulling the input low. It's called an active-low configuration. So with the cam / crank sensors, the pullup normally brings the input to +5, and when the sensor activates, it pulls the input down to ground.

The stock ECU will still need some kind of O2 sensor or it'll throw a code. You can use a stock sensor, or configure one of the outputs of the LC1 for narrowband emulation and give the ECU that signal.