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Old 03-13-2008, 06:51 PM   #1
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Default MS pigtail--->factory harness questions

Car 1994, stock. Iím installing MS slowly and (hopefully) methodically by way of the schematics here and Brainís hugely helpful MS how-to.

The original goal was to go standalone since I have no A/C. In place are the miata ignition mods, the fan mod and the IAC transistor.

The following is a list of circuits that are wired to the stock ecu and would not be accounted for (or operated by) a standalone MS, as far as I can see in the available documentation.

Things I donít care about:
EGR vent solenoid
EGR vac. solenoid
EGR function sensor
charcoal can purge
rear defrost relay
* vehicle speed sensor (whatís this? a/t only?)
steering pressure sensor

The well documented items:
a/c relay
condenser fan relay (a/c)
refrigerant pressure switch (a/c)

* The items which seem important to me but Iím not clear about (the reason for my post):
heater control unit (whatís this do?)
pressure regulator control solenoid (fuel pressure drop at idle?)
malfunction indicator (cel?)
TNS relay (wtf is this?)
3 (of 6) wires at the data link connector not accounted for
main fuse block (+12 to ecu) 1C violet wire (the only indicated hot lead in the MS docs seems to be the ecu-controlled +12 wht/red)

Iím starting to think parallel is the better strategy.

* Is there ANY degradation of signal accuracy when the signals (low voltage) are shared by two ecuís? Just making sureÖ.

* Would it be fair to assume there would be zero drawbacks to running parallel units?

* = my questions

Thanks again for everyoneís help
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Old 03-13-2008, 06:52 PM   #2
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You can do either on your 94 without issue.
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Old 03-13-2008, 10:50 PM   #3
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Of the items you're uncertain about:

* Heater control unit is an input to the ECU (active-low) that tells the ECU that the cabin fan is switched to one of the three higher speeds.

* PRC solenoid... No clue, apart from a note that it's on or near the front of the engine.

* Malfunction indicator is indeed the CEL. It's an active-low output.

* TNS Relay is the relay that turns on the parking lights, side marker lights, and taillights. No idea why the ECU cares about this, but it's an active-high signal.

* The violet wire at 1C comes from the starter. It tells the ECU that the starter is cranking. MS doesn't need this- it infers it from RPM.

* No idea about your datalink wires. They're not important.

It's probably be easier to discuss the wires you do need to run to the MS for a standalone installation, rather than the ones you don't.

You need:
1- Power (switched only)
2- Ground. Lots of 'em. Big ones. Wired straight to the head.
3- CKP and CMP from CAS.
4- Intake and Coolant temperature
5- TPS (both signal and Vref)
6- Wideband O2
7- Fan relay
8- Fuel pump relay
9- Idle solenoid
10- Spark x2
11- Injector x2

Things you should also provision for while you're in there:
1- EBC output
2- Knock input
3- WI driver (relay and PWM) if you plan to use it

That's about it.
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Old 03-14-2008, 12:22 AM   #4
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Awesome Joe. Thanks.

I'm covered on the "needed" items... and the "uncertain" items have now been cleared.

Much appreciated.
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Old 03-14-2008, 01:12 AM   #5
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Do full standalone, with no A/C on a 94 theres NO reason to do a parallel install.

I'm running full standalone on my 95.5 so not everything will be identical, but I've got a spreadsheet that I'd be more than happy to share with you about my wiring on the car.

Keep in mind that it won't be 100% identical, but you should get 99% with that sheet. I'm sure you know what the 1A, 1B, etc correspond to but just in case..

From Scott's DIY Thread.

Lastly, if you'd like to make yourself a PnP harness I have a spare 60 pin connector that I might be willing to give up. Good luck!
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