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.
Install modifications
Steps on the car itself, outside the harness. Every harness for this car inherits them.
- Re-route the pressure-sensor vacuum hose to the intake manifoldrequired
Re-route the pressure sensor's (Mazda "EGR boost sensor", pin 3S) vacuum hose directly to the intake manifold, bypassing the EGR boost solenoid. The stock ECU multiplexes baro + MAP through that solenoid: with it off the sensor reads atmosphere, with it energized it reads manifold (2000 FSM P0107/P0108). After re-routing the sensor reads MAP only, so the standalone needs its own barometric source — its onboard baro sensor if fitted, or a separate baro sensor on a spare analog input. (Alternative, not recommended: keep the hose stock and have the ECU energize the solenoid permanently via a low-side output switched with ignition; this costs an output.)
Why: With the solenoid off (its default) the sensor reads atmospheric pressure, not manifold pressure, so a standalone that uses this sensor as its MAP input would read the wrong value.
Where: EGR boost solenoid and the pressure sensor's vacuum hose (sensor signal 3S).
Source: 2000 Mazda MX-5 Miata factory service manual — engine self-diagnostics (DTC P0106/P0107/P0108)
Components
| Ref | Kind | Part | Exclude from BOM |
|---|---|---|---|
| MAIN-R | connector | ||
| NEW-BATT | terminal | ||
| NEW-KEYON | terminal | ||
| NEXUSS3-A | connector | ||
| NEXUSS3-C | connector | ||
| OEM-1 | connector | ||
| OEM-2 | connector | ||
| OEM-3 | connector | ||
| SP-0V | splice | ||
| SP-14V | splice | ||
| SP-GND | splice |
Create part
Cut list
Lengths need a layout (0 of 54 routed).
| Wire | From / To | Gauge | Signal |
|---|---|---|---|
| W1 | OEM-1-B / SP-14V-1 | 0.85 | ECU power +14V (main relay) |
| W2 | OEM-3-M / SP-14V-1 | 0.85 | ISC valve +14V feed |
| W3 | NEW-KEYON-1 / MAIN-R-COIL+ | 0.5 | Relay coil positive (ignition-switched +12V) |
| W4 | NEW-BATT-1 / MAIN-R-IN | 0.85 | Relay contact input (battery + via main fuse) |
| W5 | MAIN-R-COIL- / SP-GND-1 | 0.5 | Relay coil negative (ECU low-side driver) |
| W6 | MAIN-R-OUT / NEXUSS3-A-18 | 0.85 | Relay contact output (switched +12V bus) |
| W7 | MAIN-R-OUT / NEXUSS3-A-25 | 0.85 | Relay contact output (switched +12V bus) |
| W8 | OEM-3-A / SP-GND-1 | 0.85 | Power ground |
| W9 | OEM-3-B / SP-GND-1 | 0.85 | Power ground |
| W10 | OEM-3-C / SP-GND-1 | 0.85 | Power ground |
| W11 | SP-GND-1 / NEXUSS3-A-10 | 0.85 | Battery ground |
| W12 | SP-GND-1 / NEXUSS3-A-11 | 0.85 | Battery ground |
| W13 | OEM-3-F / SP-0V-1 | 0.5 | Signal ground |
| W14 | SP-0V-1 / NEXUSS3-C-26 | 0.5 | Signal ground |
| W15 | OEM-2-I / NEXUSS3-C-25 | 0.5 | +5V sensor supply |
| W16 | OEM-2-J / NEXUSS3-C-1 | 0.5 | Crank position (CKP) |
| W17 | SP-0V-1 / NEXUSS3-C-2 | 0.5 | Trigger - |
| W18 | OEM-2-H / NEXUSS3-C-3 | 0.5 | Cam position (CMP) |
| W19 | SP-0V-1 / NEXUSS3-C-4 | 0.5 | Home - |
| W20 | OEM-2-F / NEXUSS3-C-23 | 0.5 | Knock sensor |
| W21 | OEM-3-G / NEXUSS3-A-27 | 0.5 | Ignition 1 (coils 1+4, wasted spark) |
| W22 | OEM-3-H / NEXUSS3-A-28 | 0.5 | Ignition 2 (coils 2+3, wasted spark) |
| W23 | OEM-3-W / NEXUSS3-A-1 | 0.5 | Injector 1 |
| W24 | OEM-3-X / NEXUSS3-A-2 | 0.5 | Injector 2 |
| W25 | OEM-3-Y / NEXUSS3-A-3 | 0.5 | Injector 3 |
| W26 | OEM-3-Z / NEXUSS3-A-4 | 0.5 | Injector 4 |
| W27 | OEM-2-L / NEXUSS3-C-10 | 0.5 | Mass air flow (MAF) |
| W28 | OEM-3-E / NEXUSS3-C-11 | 0.5 | Throttle position (TPS) |
| W29 | OEM-2-E / NEXUSS3-C-12 | 0.5 | Coolant temperature (ECT) |
| W30 | OEM-1-I / NEXUSS3-A-26 | 0.5 | Condenser fan relay |
| W31 | OEM-1-R / NEXUSS3-A-9 | 0.5 | Cooling fan relay |
| W32 | OEM-1-S / NEXUSS3-A-12 | 0.5 | A/C clutch relay |
| W33 | OEM-3-N / NEXUSS3-A-14 | 0.5 | Fuel pump relay |
| W34 | OEM-1-U / NEXUSS3-C-33 | 0.5 | Front O2 heater |
| W35 | OEM-3-V / NEXUSS3-A-15 | 0.5 | Rear O2 heater |
| W36 | OEM-3-O / NEXUSS3-A-16 | 0.5 | ISC valve low side |
| W37 | OEM-1-E / NEXUSS3-A-17 | 0.5 | Malfunction indicator lamp (MIL) |
| W38 | OEM-1-O / NEXUSS3-A-5 | 0.5 | Alternator control |
| W39 | OEM-1-Q / NEXUSS3-A-6 | 0.5 | Charge lamp |
| W40 | OEM-2-M / NEXUSS3-A-7 | 0.5 | EGR valve |
| W41 | OEM-2-N / NEXUSS3-A-8 | 0.5 | EGR valve |
| W42 | OEM-3-S / NEXUSS3-C-13 | 0.5 | Pressure sensor (Mazda: EGR boost sensor) |
| W43 | OEM-2-C / NEXUSS3-C-14 | 0.5 | Front O2 signal |
| W44 | OEM-3-J / NEXUSS3-C-15 | 0.5 | Rear O2 signal |
| W45 | OEM-2-B / NEXUSS3-C-16 | 0.5 | Intake air temperature (IAT) |
| W46 | OEM-2-A / NEXUSS3-C-17 | 0.5 | Fuel tank pressure |
| W47 | OEM-3-K / NEXUSS3-C-18 | 0.5 | Fuel level |
| W48 | OEM-2-D / NEXUSS3-C-5 | 0.5 | Vehicle speed |
| W49 | OEM-1-F / NEXUSS3-C-6 | 0.5 | Brake switch |
| W50 | OEM-1-G / NEXUSS3-C-7 | 0.5 | Power steering pressure switch |
| W51 | OEM-1-P / NEXUSS3-C-8 | 0.5 | A/C request |
| W52 | OEM-1-V / NEXUSS3-C-19 | 0.5 | Neutral switch |
| W53 | OEM-3-I / NEXUSS3-C-20 | 0.5 | Clutch switch |
| W54 | NEW-KEYON-1 / NEXUSS3-A-13 | 0.5 | Ignition switch input |
Bill of materials
No wire parts assigned: 54 wires need a wire part.
| Part number | Manufacturer | Description | Qty | Unit | Unit price | Buy |
|---|---|---|---|---|---|---|
| connector3 lines | ||||||
| 174514-6 | TE | AMP Multilock .040/.070 hybrid 16-pin female harness plug (Miata NB1 ECU) | 1 | ea | Mouser ↗Digi-Key ↗Amazon ↗ | |
| 174515-6 | TE | AMP Multilock .040/.070 hybrid 22-pin female harness plug (Miata NA/NB ECU) | 1 | ea | Mouser ↗Digi-Key ↗Amazon ↗ | |
| 174516-6 | TE | AMP Multilock .040/.070 hybrid 26-pin female harness plug (Miata NA/NB ECU) | 1 | ea | Mouser ↗Digi-Key ↗Amazon ↗ | |