MS3X 90-93 - Assembling harness adaptor (grounds) - Miata Turbo Forum - Boost cars, acquire cats.

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Old 11-23-2014, 03:27 PM   #1
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Question MS3X 90-93 - Assembling harness adaptor (grounds)

I'm cross-posting this from since there seems to be more MS activity here...

I bought a DIYAutotune pre-assembled MS3X v3.57 w/ Main and MS3X harnesses as well as IAT and internal knock module back in the Spring. First-time MS user, chose to not assemble from components due to time. It's pretty much Winter, so I finally have some time to begin the wiring and installation...


`90 Miata chassis, original 1.6 B6 engine
I/H/E, will delete AFM to run MAP
Will run Sequential Fuel, stock coils for now
Innovate LC-1 wideband
DIY harness adaptor - 64-pin Male Connector, TE/AMP 174518-7
MS v3.57 Generic External harness, MS3X harness
Frank's Westfield MS3X pinout

I'm wanting to confirm I understand the ground wire situation w/ the MS3X...

Main Harness
MS3X Harness
Chassis Harness

Question 1: On my DB37 main harness, there are no pins in the DB37 connector body from 8 thru 14 -- connecting Main 8 & 9 to chassis pin 2B and Main 10 & 11 to chassis pin 2A (per Frank's pinout) appears moot. So combine MS3X-2 & 3 onto pin 2A and MS3X-8 & 12 onto pin 2B w/ nothing else from the Main harness?

Question 2a: Crank Input, Sensor Grounds. Crank Input = Main 24, on chassis pin 2E, WHT from WHT/BLK twisted pair; Crank Signal Ground = Main 1, going to chassis pin 2C, BLK from the WHT/BLK twisted pair. Frank's pinout then says another Sensor Ground, Main 2, on 2D; Main 2 = shield wire from WHT/BLK twisted this not grounded through the DB37 internally to the MS3?

Question 2b: If that's the case, what goes on 2D -- Main 7, Sensor Return, BLK/WHT? Sensors will be grounded back at the MS3, not the chassis, so it seems reasonable this will ground any low-current signals back to the MS3 via 2D...

I'm aware of the importance of these grounds, so I'd rather not mess these up and run into issues on first-start. Let me know if I'm overthinking this, as well. Thanks for any assistance.
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Old 11-26-2014, 09:47 AM   #2
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Since this is my first Megasquirt, I tried to post my questions as clearly as possible. I feel I did that. Perhaps the answers to my questions are too obvious?

Please tell me my thought process is flawed or my harness isn't wired correctly.
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