MX-5 Miata NA8 1994-95 (BP-ZE, 1.8, OBD-I) → Haltech Nexus S3 HT-213000 (auto)
MX-5 Miata NA8 1994-95 (BP-ZE, 1.8, OBD-I) — Haltech — Nexus S3
Drawn by Michael Gnankou · Rev 0 · proposal · 2026-10-12
Before you start
Not confident with automotive wiring? Have a professional harness builder or tuner do it, or check your work before first power-up. A wiring mistake can damage the ECU, the engine or the car, or start a fire.
| Status | proposal · not yet verified: nobody has reported building and running this harness |
|---|---|
| Open errors | none |
| Size of the job | 43 wires · 7 connectors · 2 part lines |
| Tools | Crimp and extraction tools for each terminal family (see Connectors) · wire strippers · multimeter · heat gun + heat-shrink |
| Order of work | 1. Check every part against the parts list. 2. Cut and label every wire (labels: Export → Wire labels). 3. Crimp and pin connector by connector, ticking the build checklist. 4. Run the bench test with nothing plugged in and the battery disconnected. 5. Only then connect the ECU and power up. |
Build checklist
Tick each box as you go. Continuity: meter from end to end, expect under 1 Ω.
| Wire | From | To | Gauge | Colour | Cut | Label | Crimp A | Crimp B | Pin A | Pin B | Continuity |
|---|---|---|---|---|---|---|---|---|---|---|---|
| W1 | OEM-1-B | SP-14V-1 | 0.85 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W2 | SP-14V-1 | NEXUSS3-A-18 | 0.85 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W3 | SP-14V-1 | NEXUSS3-A-25 | 0.85 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W4 | OEM-2-A | SP-GND-1 | 0.85 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W5 | OEM-2-B | SP-GND-1 | 0.85 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W6 | SP-GND-1 | NEXUSS3-A-10 | 0.85 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W7 | SP-GND-1 | NEXUSS3-A-11 | 0.85 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W8 | OEM-2-C | SP-0V-1 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W9 | OEM-2-D | SP-0V-1 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W10 | OEM-2-F | SP-0V-1 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W11 | SP-0V-1 | NEXUSS3-C-26 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W12 | OEM-2-K | NEXUSS3-C-25 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W13 | OEM-2-E | NEXUSS3-C-1 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W14 | SP-0V-1 | NEXUSS3-C-2 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W15 | OEM-2-G | NEXUSS3-C-3 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W16 | SP-0V-1 | NEXUSS3-C-4 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W17 | OEM-1-G | NEXUSS3-A-27 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W18 | OEM-1-H | NEXUSS3-A-28 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W19 | OEM-2-U | NEXUSS3-A-1 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W20 | OEM-2-V | NEXUSS3-A-2 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W21 | OEM-2-Y | NEXUSS3-A-3 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W22 | OEM-2-Z | NEXUSS3-A-4 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W23 | OEM-2-O | NEXUSS3-C-10 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W24 | OEM-2-M | NEXUSS3-C-11 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W25 | OEM-2-Q | NEXUSS3-C-12 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W26 | OEM-1-J | NEXUSS3-A-26 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W27 | OEM-1-R | NEXUSS3-A-9 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W28 | OEM-2-S | NEXUSS3-A-12 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W29 | OEM-2-T | NEXUSS3-A-14 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W30 | OEM-1-L | NEXUSS3-A-15 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W31 | OEM-2-L | NEXUSS3-A-16 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W32 | OEM-2-W | NEXUSS3-A-17 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W33 | OEM-1-E | NEXUSS3-C-33 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W34 | OEM-2-R | NEXUSS3-A-5 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W35 | OEM-2-X | NEXUSS3-A-6 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W36 | OEM-2-N | NEXUSS3-C-13 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W37 | OEM-2-P | NEXUSS3-C-14 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W38 | OEM-1-M | NEXUSS3-C-5 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W39 | OEM-1-C | NEXUSS3-C-6 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W40 | OEM-1-O | NEXUSS3-C-7 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W41 | OEM-1-P | NEXUSS3-C-8 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W42 | OEM-1-Q | NEXUSS3-C-19 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W43 | OEM-1-V | NEXUSS3-C-20 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ |
Bench test (before first power-up)
Battery disconnected, ECU and every sensor unplugged. Meter on resistance. Each pair below must read open (OL): a reading means a pinched wire, a stray strand or a mis-pinned cavity. Then check continuity of every wire (last column of the build checklist).
| # | Probe A | Probe B | Expect | Why | Reading |
|---|---|---|---|---|---|
| 1 | NEXUSS3-A-18 | NEXUSS3-A-10 | open (OL) | +12 V supply must not touch power ground | |
| 2 | NEXUSS3-A-18 | NEXUSS3-C-2 | open (OL) | +12 V supply must not touch sensor ground | |
| 3 | NEXUSS3-A-10 | NEXUSS3-C-25 | open (OL) | power ground must not touch 5 V sensor reference | |
| 4 | NEXUSS3-A-18 | NEXUSS3-C-25 | open (OL) | +12 V supply must not touch 5 V sensor reference | |
| 5 | NEXUSS3-C-2 | NEXUSS3-C-25 | open (OL) | sensor ground must not touch 5 V sensor reference |
If any reading doesn't match, stop and get help before powering up.
Revisions
| Rev | Label | By | Date |
|---|---|---|---|
| No revisions yet. | |||
Schematic
Connectors
NEXUSS3-A
| Cavity | Function | Signal | Wire | Colour | Gauge (mm²) | Destination | Terminal | Seal | Plug |
|---|---|---|---|---|---|---|---|---|---|
| 1 | Injector 1 | — | W19 | — | 0.5 | OEM-2-U | — | — | — |
| 10 | Battery ground | — | W6 | — | 0.85 | SP-GND-1 | — | — | — |
| 11 | Battery ground | — | W7 | — | 0.85 | SP-GND-1 | — | — | — |
| 12 | DPO 2 | — | W28 | — | 0.5 | OEM-2-S | — | — | — |
| 13 | Ignition switch input | — | — | — | — | — | — | — | — |
| 14 | DPO 3 | — | W29 | — | 0.5 | OEM-2-T | — | — | — |
| 15 | DPO 4 | — | W30 | — | 0.5 | OEM-1-L | — | — | — |
| 16 | DPO 5 | — | W31 | — | 0.5 | OEM-2-L | — | — | — |
| 17 | DPO 6 | — | W32 | — | 0.5 | OEM-2-W | — | — | — |
| 18 | +12V switched input | — | W2 | — | 0.85 | SP-14V-1 | — | — | — |
| 19 | HBO 1 | — | — | — | — | — | — | — | — |
| 2 | Injector 2 | — | W20 | — | 0.5 | OEM-2-V | — | — | — |
| 20 | HBO 2 | — | — | — | — | — | — | — | — |
| 21 | HBO 3 | — | — | — | — | — | — | — | — |
| 22 | HBO 4 | — | — | — | — | — | — | — | — |
| 23 | CAN 1 High | — | — | — | — | — | — | — | — |
| 24 | CAN 1 Low | — | — | — | — | — | — | — | — |
| 25 | +12V switched input | — | W3 | — | 0.85 | SP-14V-1 | — | — | — |
| 26 | ECR output | — | W26 | — | 0.5 | OEM-1-J | — | — | — |
| 27 | Ignition 1 | — | W17 | — | 0.5 | OEM-1-G | — | — | — |
| 28 | Ignition 2 | — | W18 | — | 0.5 | OEM-1-H | — | — | — |
| 29 | Ignition 3 | — | — | — | — | — | — | — | — |
| 3 | Injector 3 | — | W21 | — | 0.5 | OEM-2-Y | — | — | — |
| 30 | Ignition 4 | — | — | — | — | — | — | — | — |
| 31 | Ignition 5 | — | — | — | — | — | — | — | — |
| 32 | Ignition 6 | — | — | — | — | — | — | — | — |
| 33 | Ignition 7 | — | — | — | — | — | — | — | — |
| 34 | Ignition 8 | — | — | — | — | — | — | — | — |
| 4 | Injector 4 | — | W22 | — | 0.5 | OEM-2-Z | — | — | — |
| 5 | Injector 5 | — | W34 | — | 0.5 | OEM-2-R | — | — | — |
| 6 | Injector 6 | — | W35 | — | 0.5 | OEM-2-X | — | — | — |
| 7 | Injector 7 | — | — | — | — | — | — | — | — |
| 8 | Injector 8 | — | — | — | — | — | — | — | — |
| 9 | DPO 1 | — | W27 | — | 0.5 | OEM-1-R | — | — | — |
NEXUSS3-C
| Cavity | Function | Signal | Wire | Colour | Gauge (mm²) | Destination | Terminal | Seal | Plug |
|---|---|---|---|---|---|---|---|---|---|
| 1 | Trigger + | — | W13 | — | 0.5 | OEM-2-E | — | — | — |
| 10 | AVI 1 | — | W23 | — | 0.5 | OEM-2-O | — | — | — |
| 11 | AVI 2 | — | W24 | — | 0.5 | OEM-2-M | — | — | — |
| 12 | AVI 3 | — | W25 | — | 0.5 | OEM-2-Q | — | — | — |
| 13 | AVI 4 | — | W36 | — | 0.5 | OEM-2-N | — | — | — |
| 14 | AVI 5 | — | W37 | — | 0.5 | OEM-2-P | — | — | — |
| 15 | AVI 6 | — | — | — | — | — | — | — | — |
| 16 | AVI 7 | — | — | — | — | — | — | — | — |
| 17 | AVI 8 | — | — | — | — | — | — | — | — |
| 18 | AVI 9 | — | — | — | — | — | — | — | — |
| 19 | SPI 5 | — | W42 | — | 0.5 | OEM-1-Q | — | — | — |
| 2 | Trigger - | — | W14 | — | 0.5 | SP-0V-1 | — | — | — |
| 20 | SPI 6 | — | W43 | — | 0.5 | OEM-1-V | — | — | — |
| 21 | CAN 2 High | — | — | — | — | — | — | — | — |
| 22 | CAN 2 Low | — | — | — | — | — | — | — | — |
| 23 | Knock 1 | — | — | — | — | — | — | — | — |
| 24 | Knock 2 | — | — | — | — | — | — | — | — |
| 25 | +5V | — | W12 | — | 0.5 | OEM-2-K | — | — | — |
| 26 | Signal ground | — | W11 | — | 0.5 | SP-0V-1 | — | — | — |
| 27 | AVI 10 | — | — | — | — | — | — | — | — |
| 28 | AVI 11 | — | — | — | — | — | — | — | — |
| 29 | WBI 1 Heater + | — | — | — | — | — | — | — | — |
| 3 | Home + | — | W15 | — | 0.5 | OEM-2-G | — | — | — |
| 30 | WBI 1 Input | — | — | — | — | — | — | — | — |
| 31 | WBI 1 Pump | — | — | — | — | — | — | — | — |
| 32 | WBI 1 Nernst | — | — | — | — | — | — | — | — |
| 33 | WBI 1 Heater - | — | W33 | — | 0.5 | OEM-1-E | — | — | — |
| 34 | WBI 1 Cal | — | — | — | — | — | — | — | — |
| 4 | Home - | — | W16 | — | 0.5 | SP-0V-1 | — | — | — |
| 5 | SPI 1 | — | W38 | — | 0.5 | OEM-1-M | — | — | — |
| 6 | SPI 2 | — | W39 | — | 0.5 | OEM-1-C | — | — | — |
| 7 | SPI 3 | — | W40 | — | 0.5 | OEM-1-O | — | — | — |
| 8 | SPI 4 | — | W41 | — | 0.5 | OEM-1-P | — | — | — |
| 9 | +8V | — | — | — | — | — | — | — | — |
OEM-1
| Cavity | Function | Signal | Wire | Colour | Gauge (mm²) | Destination | Terminal | Seal | Plug |
|---|---|---|---|---|---|---|---|---|---|
| A | Constant +12V | — | — | — | — | — | — | — | — |
| B | ECU power +14V (main relay) | — | W1 | — | 0.85 | SP-14V-1 | — | — | — |
| C | Start signal | — | W39 | — | 0.5 | NEXUSS3-C-6 | — | — | — |
| D | Data link connector | — | — | — | — | — | — | — | — |
| E | Malfunction indicator lamp (MIL) | — | W33 | — | 0.5 | NEXUSS3-C-33 | — | — | — |
| G | Ignition 1 (coils 1+4, wasted spark) | — | W17 | — | 0.5 | NEXUSS3-A-27 | — | — | — |
| H | Ignition 2 (coils 2+3, wasted spark) | — | W18 | — | 0.5 | NEXUSS3-A-28 | — | — | — |
| I | Powertrain control module (transmission) | — | — | — | — | — | — | — | — |
| J | A/C relay | — | W26 | — | 0.5 | NEXUSS3-A-26 | — | — | — |
| L | Coolant fan relay | — | W30 | — | 0.5 | NEXUSS3-A-15 | — | — | — |
| M | Vehicle speed | — | W38 | — | 0.5 | NEXUSS3-C-5 | — | — | — |
| N | Powertrain control module (transmission) | — | — | — | — | — | — | — | — |
| O | Stop light switch | — | W40 | — | 0.5 | NEXUSS3-C-7 | — | — | — |
| P | Power steering pressure switch | — | W41 | — | 0.5 | NEXUSS3-C-8 | — | — | — |
| Q | A/C request | — | W42 | — | 0.5 | NEXUSS3-C-19 | — | — | — |
| R | Cooling fan relay | — | W27 | — | 0.5 | NEXUSS3-A-9 | — | — | — |
| S | Heater control unit | — | — | — | — | — | — | — | — |
| T | Unknown | — | — | — | — | — | — | — | — |
| U | Unknown | — | — | — | — | — | — | — | — |
| V | Neutral/clutch switch | — | W43 | — | 0.5 | NEXUSS3-C-20 | — | — | — |
OEM-2
| Cavity | Function | Signal | Wire | Colour | Gauge (mm²) | Destination | Terminal | Seal | Plug |
|---|---|---|---|---|---|---|---|---|---|
| A | Power ground | — | W4 | — | 0.85 | SP-GND-1 | — | — | — |
| B | Power ground | — | W5 | — | 0.85 | SP-GND-1 | — | — | — |
| C | Sensor ground (E2) | — | W8 | — | 0.5 | SP-0V-1 | — | — | — |
| D | Sensor ground (E2) | — | W9 | — | 0.5 | SP-0V-1 | — | — | — |
| E | Crank position (CAS NE) | — | W13 | — | 0.5 | NEXUSS3-C-1 | — | — | — |
| F | MAF ground | — | W10 | — | 0.5 | SP-0V-1 | — | — | — |
| G | Cam position (CAS G) | — | W15 | — | 0.5 | NEXUSS3-C-3 | — | — | — |
| H | Data link connector | — | — | — | — | — | — | — | — |
| I | Tachometer output | — | — | — | — | — | — | — | — |
| J | EGR function sensor | — | — | — | — | — | — | — | — |
| K | +5V sensor supply | — | W12 | — | 0.5 | NEXUSS3-C-25 | — | — | — |
| L | Rear defroster relay | — | W31 | — | 0.5 | NEXUSS3-A-16 | — | — | — |
| M | Throttle position (TPS) | — | W24 | — | 0.5 | NEXUSS3-C-11 | — | — | — |
| N | O2 sensor | — | W36 | — | 0.5 | NEXUSS3-C-13 | — | — | — |
| O | Mass air flow (MAF) | — | W23 | — | 0.5 | NEXUSS3-C-10 | — | — | — |
| P | Intake air temperature (IAT) | — | W37 | — | 0.5 | NEXUSS3-C-14 | — | — | — |
| Q | Coolant temperature (ECT) | — | W25 | — | 0.5 | NEXUSS3-C-12 | — | — | — |
| R | PRC solenoid (fuel pressure regulator) | — | W34 | — | 0.5 | NEXUSS3-A-5 | — | — | — |
| S | Condenser fan relay | — | W28 | — | 0.5 | NEXUSS3-A-12 | — | — | — |
| T | Fuel pump relay | — | W29 | — | 0.5 | NEXUSS3-A-14 | — | — | — |
| U | Injector 1 | — | W19 | — | 0.5 | NEXUSS3-A-1 | — | — | — |
| V | Injector 2 | — | W20 | — | 0.5 | NEXUSS3-A-2 | — | — | — |
| W | ISC solenoid | — | W32 | — | 0.5 | NEXUSS3-A-17 | — | — | — |
| X | Evap purge solenoid | — | W35 | — | 0.5 | NEXUSS3-A-6 | — | — | — |
| Y | Injector 3 | — | W21 | — | 0.5 | NEXUSS3-A-3 | — | — | — |
| Z | Injector 4 | — | W22 | — | 0.5 | NEXUSS3-A-4 | — | — | — |
SP-0V
| Cavity | Function | Signal | Wire | Colour | Gauge (mm²) | Destination | Terminal | Seal | Plug |
|---|---|---|---|---|---|---|---|---|---|
| 1 | — | — | W8 | — | 0.5 | OEM-2-C | — | — | — |
| 1 | — | — | W9 | — | 0.5 | OEM-2-D | — | — | — |
| 1 | — | — | W10 | — | 0.5 | OEM-2-F | — | — | — |
| 1 | — | — | W11 | — | 0.5 | NEXUSS3-C-26 | — | — | — |
| 1 | — | — | W14 | — | 0.5 | NEXUSS3-C-2 | — | — | — |
| 1 | — | — | W16 | — | 0.5 | NEXUSS3-C-4 | — | — | — |
SP-14V
| Cavity | Function | Signal | Wire | Colour | Gauge (mm²) | Destination | Terminal | Seal | Plug |
|---|---|---|---|---|---|---|---|---|---|
| 1 | — | — | W1 | — | 0.85 | OEM-1-B | — | — | — |
| 1 | — | — | W2 | — | 0.85 | NEXUSS3-A-18 | — | — | — |
| 1 | — | — | W3 | — | 0.85 | NEXUSS3-A-25 | — | — | — |
SP-GND
| Cavity | Function | Signal | Wire | Colour | Gauge (mm²) | Destination | Terminal | Seal | Plug |
|---|---|---|---|---|---|---|---|---|---|
| 1 | — | — | W4 | — | 0.85 | OEM-2-A | — | — | — |
| 1 | — | — | W5 | — | 0.85 | OEM-2-B | — | — | — |
| 1 | — | — | W6 | — | 0.85 | NEXUSS3-A-10 | — | — | — |
| 1 | — | — | W7 | — | 0.85 | NEXUSS3-A-11 | — | — | — |
Pin map
| OEM point | OEM function | OEM family | Target point | Target function | Target family | Wire colour | Evidence |
|---|---|---|---|---|---|---|---|
| OEM-1-A | Constant +12V | power_in | — | — | — | LR | single_source |
| OEM-1-B | ECU power +14V (main relay) | power_in | NEXUSS3-A-18 + NEXUSS3-A-25 | +12V switched input + +12V switched input | power_in | WR | single_source |
| OEM-1-C | Start signal | digital_in | NEXUSS3-C-6 | SPI 2 | digital_in | V | single_source |
| OEM-1-D | Data link connector | serial | — | — | — | WG | single_source |
| OEM-1-E | Malfunction indicator lamp (MIL) | low_side_out | NEXUSS3-C-33 | WBI 1 Heater - | low_side_out | YB | single_source |
| OEM-1-G | Ignition 1 (coils 1+4, wasted spark) | ignition_out | NEXUSS3-A-27 | Ignition 1 | ignition_out | BrY | single_source |
| OEM-1-H | Ignition 2 (coils 2+3, wasted spark) | ignition_out | NEXUSS3-A-28 | Ignition 2 | ignition_out | Br | single_source |
| OEM-1-I | Powertrain control module (transmission) | — | — | — | — | LW | single_source |
| OEM-1-J | A/C relay | low_side_out | NEXUSS3-A-26 | ECR output | low_side_out | single_source | |
| OEM-1-L | Coolant fan relay | low_side_out | NEXUSS3-A-15 | DPO 4 | low_side_out | BG | single_source |
| OEM-1-M | Vehicle speed | digital_in | NEXUSS3-C-5 | SPI 1 | digital_in | GR | single_source |
| OEM-1-N | Powertrain control module (transmission) | — | — | — | — | R | single_source |
| OEM-1-O | Stop light switch | digital_in | NEXUSS3-C-7 | SPI 3 | digital_in | GB | single_source |
| OEM-1-P | Power steering pressure switch | digital_in | NEXUSS3-C-8 | SPI 4 | digital_in | LY | single_source |
| OEM-1-Q | A/C request | digital_in | NEXUSS3-C-19 | SPI 5 | digital_in | LgB | single_source |
| OEM-1-R | Cooling fan relay | low_side_out | NEXUSS3-A-9 | DPO 1 | low_side_out | YB | single_source |
| OEM-1-S | Heater control unit | — | — | — | — | LOr | single_source |
| OEM-1-T | Unknown | — | — | — | — | YR | single_source |
| OEM-1-U | Unknown | — | — | — | — | RB | single_source |
| OEM-1-V | Neutral/clutch switch | digital_in | NEXUSS3-C-20 | SPI 6 | digital_in | BrW | single_source |
| OEM-2-A | Power ground | ground | NEXUSS3-A-10 + NEXUSS3-A-11 | Battery ground + Battery ground | ground | B | single_source |
| OEM-2-B | Power ground | ground | NEXUSS3-A-10 + NEXUSS3-A-11 | Battery ground + Battery ground | ground | B | single_source |
| OEM-2-C | Sensor ground (E2) | sensor_ground | NEXUSS3-C-2 + NEXUSS3-C-26 + NEXUSS3-C-4 | Trigger - + Signal ground + Home - | sensor_ground + trigger_in | BLg | corroborated |
| OEM-2-D | Sensor ground (E2) | sensor_ground | NEXUSS3-C-2 + NEXUSS3-C-26 + NEXUSS3-C-4 | Trigger - + Signal ground + Home - | sensor_ground + trigger_in | BL | corroborated |
| OEM-2-E | Crank position (CAS NE) | trigger_in | NEXUSS3-C-1 | Trigger + | trigger_in | W | single_source |
| OEM-2-F | MAF ground | sensor_ground | NEXUSS3-C-2 + NEXUSS3-C-26 + NEXUSS3-C-4 | Trigger - + Signal ground + Home - | sensor_ground + trigger_in | BR | single_source |
| OEM-2-G | Cam position (CAS G) | trigger_in | NEXUSS3-C-3 | Home + | trigger_in | YL | single_source |
| OEM-2-H | Data link connector | serial | — | — | — | LgY | single_source |
| OEM-2-I | Tachometer output | tacho_out | — | — | — | BW | single_source |
| OEM-2-J | EGR function sensor | — | — | — | — | LgR | single_source |
| OEM-2-K | +5V sensor supply | vref | NEXUSS3-C-25 | +5V | vref | LgW | single_source |
| OEM-2-L | Rear defroster relay | low_side_out | NEXUSS3-A-16 | DPO 5 | low_side_out | LR | single_source |
| OEM-2-M | Throttle position (TPS) | analog_in | NEXUSS3-C-11 | AVI 2 | analog_in | RB | single_source |
| OEM-2-N | O2 sensor | lambda_nb_in | NEXUSS3-C-13 | AVI 4 | analog_in | RL | single_source |
| OEM-2-O | Mass air flow (MAF) | analog_in | NEXUSS3-C-10 | AVI 1 | analog_in | R | single_source |
| OEM-2-P | Intake air temperature (IAT) | temp_in | NEXUSS3-C-14 | AVI 5 | analog_in | RB | single_source |
| OEM-2-Q | Coolant temperature (ECT) | temp_in | NEXUSS3-C-12 | AVI 3 | analog_in | LW | single_source |
| OEM-2-R | PRC solenoid (fuel pressure regulator) | low_side_out | NEXUSS3-A-5 | Injector 5 | injector_out | YG | single_source |
| OEM-2-S | Condenser fan relay | low_side_out | NEXUSS3-A-12 | DPO 2 | low_side_out | LW | single_source |
| OEM-2-T | Fuel pump relay | low_side_out | NEXUSS3-A-14 | DPO 3 | low_side_out | Lg | single_source |
| OEM-2-U | Injector 1 | injector_out | NEXUSS3-A-1 | Injector 1 | injector_out | Y | single_source |
| OEM-2-V | Injector 2 | injector_out | NEXUSS3-A-2 | Injector 2 | injector_out | YB | single_source |
| OEM-2-W | ISC solenoid | low_side_out | NEXUSS3-A-17 | DPO 6 | low_side_out | LOr | single_source |
| OEM-2-X | Evap purge solenoid | low_side_out | NEXUSS3-A-6 | Injector 6 | injector_out | YR | single_source |
| OEM-2-Y | Injector 3 | injector_out | NEXUSS3-A-3 | Injector 3 | injector_out | GW | single_source |
| OEM-2-Z | Injector 4 | injector_out | NEXUSS3-A-4 | Injector 4 | injector_out | G | single_source |
Cut list
| Wire | From | To | Gauge (mm²) | Colour | Length | Signal | Ident |
|---|---|---|---|---|---|---|---|
| W1 | OEM-1-B | SP-14V-1 | 0.85 | no route | ECU power +14V (main relay) | — | |
| W2 | SP-14V-1 | NEXUSS3-A-18 | 0.85 | no route | +12V switched input | — | |
| W3 | SP-14V-1 | NEXUSS3-A-25 | 0.85 | no route | +12V switched input | — | |
| W4 | OEM-2-A | SP-GND-1 | 0.85 | no route | Power ground | — | |
| W5 | OEM-2-B | SP-GND-1 | 0.85 | no route | Power ground | — | |
| W6 | SP-GND-1 | NEXUSS3-A-10 | 0.85 | no route | Battery ground | — | |
| W7 | SP-GND-1 | NEXUSS3-A-11 | 0.85 | no route | Battery ground | — | |
| W8 | OEM-2-C | SP-0V-1 | 0.5 | no route | Sensor ground (E2) | — | |
| W9 | OEM-2-D | SP-0V-1 | 0.5 | no route | Sensor ground (E2) | — | |
| W10 | OEM-2-F | SP-0V-1 | 0.5 | no route | MAF ground | — | |
| W11 | SP-0V-1 | NEXUSS3-C-26 | 0.5 | no route | Signal ground | — | |
| W12 | OEM-2-K | NEXUSS3-C-25 | 0.5 | no route | +5V sensor supply | — | |
| W13 | OEM-2-E | NEXUSS3-C-1 | 0.5 | no route | Crank position (CAS NE) | — | |
| W14 | SP-0V-1 | NEXUSS3-C-2 | 0.5 | no route | Trigger - | — | |
| W15 | OEM-2-G | NEXUSS3-C-3 | 0.5 | no route | Cam position (CAS G) | — | |
| W16 | SP-0V-1 | NEXUSS3-C-4 | 0.5 | no route | Home - | — | |
| W17 | OEM-1-G | NEXUSS3-A-27 | 0.5 | no route | Ignition 1 (coils 1+4, wasted spark) | — | |
| W18 | OEM-1-H | NEXUSS3-A-28 | 0.5 | no route | Ignition 2 (coils 2+3, wasted spark) | — | |
| W19 | OEM-2-U | NEXUSS3-A-1 | 0.5 | no route | Injector 1 | — | |
| W20 | OEM-2-V | NEXUSS3-A-2 | 0.5 | no route | Injector 2 | — | |
| W21 | OEM-2-Y | NEXUSS3-A-3 | 0.5 | no route | Injector 3 | — | |
| W22 | OEM-2-Z | NEXUSS3-A-4 | 0.5 | no route | Injector 4 | — | |
| W23 | OEM-2-O | NEXUSS3-C-10 | 0.5 | no route | Mass air flow (MAF) | — | |
| W24 | OEM-2-M | NEXUSS3-C-11 | 0.5 | no route | Throttle position (TPS) | — | |
| W25 | OEM-2-Q | NEXUSS3-C-12 | 0.5 | no route | Coolant temperature (ECT) | — | |
| W26 | OEM-1-J | NEXUSS3-A-26 | 0.5 | no route | A/C relay | — | |
| W27 | OEM-1-R | NEXUSS3-A-9 | 0.5 | no route | Cooling fan relay | — | |
| W28 | OEM-2-S | NEXUSS3-A-12 | 0.5 | no route | Condenser fan relay | — | |
| W29 | OEM-2-T | NEXUSS3-A-14 | 0.5 | no route | Fuel pump relay | — | |
| W30 | OEM-1-L | NEXUSS3-A-15 | 0.5 | no route | Coolant fan relay | — | |
| W31 | OEM-2-L | NEXUSS3-A-16 | 0.5 | no route | Rear defroster relay | — | |
| W32 | OEM-2-W | NEXUSS3-A-17 | 0.5 | no route | ISC solenoid | — | |
| W33 | OEM-1-E | NEXUSS3-C-33 | 0.5 | no route | Malfunction indicator lamp (MIL) | — | |
| W34 | OEM-2-R | NEXUSS3-A-5 | 0.5 | no route | PRC solenoid (fuel pressure regulator) | — | |
| W35 | OEM-2-X | NEXUSS3-A-6 | 0.5 | no route | Evap purge solenoid | — | |
| W36 | OEM-2-N | NEXUSS3-C-13 | 0.5 | no route | O2 sensor | — | |
| W37 | OEM-2-P | NEXUSS3-C-14 | 0.5 | no route | Intake air temperature (IAT) | — | |
| W38 | OEM-1-M | NEXUSS3-C-5 | 0.5 | no route | Vehicle speed | — | |
| W39 | OEM-1-C | NEXUSS3-C-6 | 0.5 | no route | Start signal | — | |
| W40 | OEM-1-O | NEXUSS3-C-7 | 0.5 | no route | Stop light switch | — | |
| W41 | OEM-1-P | NEXUSS3-C-8 | 0.5 | no route | Power steering pressure switch | — | |
| W42 | OEM-1-Q | NEXUSS3-C-19 | 0.5 | no route | A/C request | — | |
| W43 | OEM-1-V | NEXUSS3-C-20 | 0.5 | no route | Neutral/clutch switch | — |
Bill of materials
| Category | Part number | Manufacturer | Description | Qty | Unit |
|---|---|---|---|---|---|
| connector | 174515-6 | TE | AMP Multilock .040/.070 hybrid 22-pin female harness plug (Miata NA/NB ECU) | 1.000 | ea |
| connector | 174516-6 | TE | AMP Multilock .040/.070 hybrid 26-pin female harness plug (Miata NA/NB ECU) | 1.000 | ea |
ECU setup sheet
| Role | Engine ref | Engine signal | Sensor | ECU point | ECU function | ECU class | Setup flag |
|---|---|---|---|---|---|---|---|
| No configured channels. | |||||||
Findings
Open (7)
| Severity | Code | Subject | Message |
|---|---|---|---|
| warn | LOAD_UNKNOWN | NEXUSS3-A-26 | NEXUSS3-A-26 "ECR output" drives OEM-1-J A/C relay (load 0.2 A) but its current rating is unknown. Check the ECU manual. |
| info | NET_FAMILY | NEXUSS3-C-26 ↔ NEXUSS3-C-4 | NEXUSS3-C-26 "Signal ground" [sensor_ground] is wired to NEXUSS3-C-4 "Home -" [trigger_in]. Trigger return tied to sensor/trigger ground: correct for single-ended trigger inputs. |
| info | NET_FAMILY | OEM-2-P ↔ NEXUSS3-C-14 | OEM-2-P "Intake air temperature (IAT)" [temp_in] is wired to NEXUSS3-C-14 "AVI 5" [analog_in]. Thermistor on a plain analog input needs a pull-up; check the channel can enable one. |
| info | NET_FAMILY | OEM-2-Q ↔ NEXUSS3-C-12 | OEM-2-Q "Coolant temperature (ECT)" [temp_in] is wired to NEXUSS3-C-12 "AVI 3" [analog_in]. Thermistor on a plain analog input needs a pull-up; check the channel can enable one. |
| info | NET_FAMILY | OEM-2-R ↔ NEXUSS3-A-5 | OEM-2-R "PRC solenoid (fuel pressure regulator)" [low_side_out] is wired to NEXUSS3-A-5 "Injector 5" [injector_out]. Injector drivers can usually run general low-side loads; check current and PWM frequency. |
| info | NET_FAMILY | OEM-2-X ↔ NEXUSS3-A-6 | OEM-2-X "Evap purge solenoid" [low_side_out] is wired to NEXUSS3-A-6 "Injector 6" [injector_out]. Injector drivers can usually run general low-side loads; check current and PWM frequency. |
| info | UNMAPPED | OEM | 9 optional OEM pins are not mapped: OEM-1-D Data link connector; OEM-1-I Powertrain control module (transmission); OEM-1-N Powertrain control module (transmission); OEM-1-S Heater control unit; OEM-1-T Unknown; OEM-1-U Unknown; OEM-2-H Data link connector; OEM-2-I Tachometer output; OEM-2-J EGR function sensor |
Accepted (1)
| Code | Subject | Reason | By |
|---|---|---|---|
| REQUIRED_UNMAPPED | OEM-1-A | Battery-constant (memory) feed of the stock ECU: the new ECU has no such input, so it is not needed. | mapping-proposal |
Notes
Auto-mapped by auto_map() from the library pin data on 2026-10-11. Review every wire against both manuals before building. Not wired: - OEM-1 A: Constant +12V: Haltech Nexus S3 has no battery-constant input; not needed - OEM-2 I: Tachometer output: no free tacho/frequency_out/low_side/ls_hs on Haltech Nexus S3 - OEM-1 D: Data link connector: no free k_line on Haltech Nexus S3 - OEM-2 H: Data link connector: no free k_line on Haltech Nexus S3 - OEM-1 I: Powertrain control module (transmission): not classified in the library; wire by hand - OEM-1 N: Powertrain control module (transmission): not classified in the library; wire by hand - OEM-1 S: Heater control unit: not classified in the library; wire by hand - OEM-1 T: Unknown: not classified in the library; wire by hand - OEM-1 U: Unknown: not classified in the library; wire by hand - OEM-2 J: EGR function sensor: not classified in the library; wire by hand - NEXUSS3-A 13: Ignition switch input: not fed (the stock ECU has no ignition-sense pin); feed it from a switched-ignition source
Sources
| Reliability | Kind | Title | URL | Archive | Captured | SHA-256 |
|---|---|---|---|---|---|---|
| 4 | vendor_doc | Haltech: Nexus S3 Plug 'n' Play adapter QSG (Subaru WRX/STI ADM, HT-186300) — ECU Connector A & C pinout | https://www.haltech.com/product/ht-186300-nexus-s3-plug-n-play-adapter-harness/ | archive | 2026-10-05 | 3cab7cd337c2 |
| 4 | vendor_doc | Haltech: Nexus S3/S2 ECU Overview (QSG) — specifications | https://store.haltech.com/product/ht-213000-nexus-s3-ecu-only/ | archive | 2026-10-05 | 388299668207 |
| 4 | vendor_doc | Link G4X MX5X install manual (NA 1.6/1.8) | https://linkecu.com/documentation/MX5X.pdf | archive | 2026-10-05 | b7f730de9f6e |
| 2 | expert_report | Justin Barrera — Miata NA/NB wiring corrections | — | — | — | — |
| 2 | community_copy | rusefi wiki: 1994 Mazda Miata 1.8 (NA8) ECU pinout | https://github.com/rusefi/rusefi/wiki/Mazda-Miata-1994 | — | 2026-10-08 | 075801b907f4 |