MS pigtail--->factory harness questions
 

Car 1994, stock. I’m installing MS slowly and (hopefully) methodically by way of the schematics here and Brain’s 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 don’t care about:
EGR vent solenoid
EGR vac. solenoid
EGR function sensor
charcoal can purge
rear defrost relay
* vehicle speed sensor (what’s 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 I’m not clear about (the reason for my post):
heater control unit (what’s 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)


I’m starting to think parallel is the better strategy.

* Is there ANY degradation of signal accuracy when the signals (low voltage) are shared by two ecu’s? Just making sure….

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



* = my questions

Thanks again for everyone’s help

No
Yes

You can do either on your 94 without issue.

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.

Awesome Joe. Thanks.

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

Much appreciated.

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.

http://spreadsheets.google.com/pub?k...A0Z3FkV_q0Wjbg

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.. ;)

http://www.boostedmiata.com/MS/harness_MS_pinouts.jpg
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! :)