MX-5 Miata NB1 1999-00 (BP-4W) → Motorsport Electronics ME221 (auto)
MX-5 Miata NB1 1999-00 (BP-4W) — Motorsport Electronics — ME221
Drawn by Michael Gnankou · Rev 0 · proposal · 2026-10-09
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.
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)
| Status | proposal · not yet verified: nobody has reported building and running this harness |
|---|---|
| Open errors | none |
| Size of the job | 44 wires · 7 connectors · 3 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 | OEM-3-M | SP-14V-1 | 0.85 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W3 | SP-14V-1 | ME221-C1-15 | 0.85 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W4 | SP-14V-1 | ME221-C1-64 | 0.85 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W5 | OEM-3-A | SP-GND-1 | 0.85 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W6 | OEM-3-B | SP-GND-1 | 0.85 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W7 | OEM-3-C | SP-GND-1 | 0.85 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W8 | SP-GND-1 | ME221-C1-10 | 0.85 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W9 | SP-GND-1 | ME221-C1-61 | 0.85 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W10 | SP-GND-1 | ME221-C1-89 | 0.85 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W11 | SP-GND-1 | ME221-C1-90 | 0.85 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W12 | OEM-3-F | SP-0V-1 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W13 | SP-0V-1 | ME221-C1-52 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W14 | SP-0V-1 | ME221-C1-84 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W15 | OEM-2-I | ME221-C1-45 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W16 | OEM-2-J | ME221-C1-81 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W17 | OEM-2-H | ME221-C1-22 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W18 | OEM-2-F | ME221-C1-53 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W19 | OEM-3-G | ME221-C1-32 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W20 | OEM-3-H | ME221-C1-31 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W21 | OEM-3-W | ME221-C1-63 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W22 | OEM-3-X | ME221-C1-4 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W23 | OEM-3-Y | ME221-C1-33 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W24 | OEM-3-Z | ME221-C1-3 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W25 | OEM-1-I | ME221-C1-73 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W26 | OEM-1-R | ME221-C1-12 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W27 | OEM-1-S | ME221-C1-74 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W28 | OEM-3-N | ME221-C1-44 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W29 | OEM-1-U | ME221-C1-16 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W30 | OEM-3-V | ME221-C1-69 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W31 | OEM-3-O | ME221-C1-39 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W32 | OEM-1-E | ME221-C1-67 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W33 | OEM-1-O | ME221-C1-68 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W34 | OEM-1-Q | ME221-C1-70 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W35 | OEM-2-M | ME221-C1-71 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W36 | OEM-2-K | ME221-C1-79 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W37 | OEM-2-L | ME221-C1-26 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W38 | OEM-3-S | ME221-C1-56 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W39 | OEM-3-E | ME221-C1-17 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W40 | OEM-2-C | ME221-C1-18 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W41 | OEM-2-E | ME221-C1-86 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W42 | OEM-2-B | ME221-C1-57 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W43 | OEM-2-D | ME221-C1-6 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | |
| W44 | OEM-1-F | ME221-C1-7 | 0.5 | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ | ☐ |
Bench test (before first power-up)
Pre-power install steps (make these cuts/modifications on the car first, then verify the checks below): Re-route the pressure-sensor vacuum hose to the intake manifold.
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 | ME221-C1-15 | ME221-C1-10 | open (OL) | +12 V supply must not touch power ground | |
| 2 | ME221-C1-15 | ME221-C1-52 | open (OL) | +12 V supply must not touch sensor ground | |
| 3 | ME221-C1-45 | ME221-C1-10 | open (OL) | 5 V sensor reference must not touch power ground | |
| 4 | ME221-C1-45 | ME221-C1-52 | open (OL) | 5 V sensor reference must not touch sensor ground | |
| 5 | ME221-C1-15 | ME221-C1-45 | open (OL) | +12 V supply 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
ME221-C1
| Cavity | Function | Signal | Wire | Colour | Gauge (mm²) | Destination | Terminal | Seal | Plug |
|---|---|---|---|---|---|---|---|---|---|
| 1 | COIL 4 | — | — | — | — | — | — | — | — |
| 10 | GROUND CHASSIS | — | W8 | — | 0.85 | SP-GND-1 | — | — | — |
| 12 | LOW SIDE 2 | — | W26 | — | 0.5 | OEM-1-R | — | — | — |
| 14 | LSU +12V | — | — | — | — | — | — | — | — |
| 15 | IGN +12V | — | W3 | — | 0.85 | SP-14V-1 | — | — | — |
| 16 | LSU HEATER -VE | — | W29 | — | 0.5 | OEM-1-U | — | — | — |
| 17 | ANA VOLT 3 | — | W39 | — | 0.5 | OEM-3-E | — | — | — |
| 18 | ANA VOLT 4 | — | W40 | — | 0.5 | OEM-2-C | — | — | — |
| 19 | LSU UN | — | — | — | — | — | — | — | — |
| 2 | COIL 3 | — | — | — | — | — | — | — | — |
| 20 | LSU VM | — | — | — | — | — | — | — | — |
| 21 | CAN 1 HIGH | — | — | — | — | — | — | — | — |
| 22 | CAM A VR+ | — | W17 | — | 0.5 | OEM-2-H | — | — | — |
| 23 | CAM A VR- | — | — | — | — | — | — | — | — |
| 24 | SERIAL 1 GROUND | — | — | — | — | — | — | — | — |
| 25 | SERIAL 1 TX | — | — | — | — | — | — | — | — |
| 26 | ANA VOLT 1 | — | W37 | — | 0.5 | OEM-2-L | — | — | — |
| 3 | INJECTOR 4 | — | W24 | — | 0.5 | OEM-3-Z | — | — | — |
| 31 | COIL 2 | — | W20 | — | 0.5 | OEM-3-H | — | — | — |
| 32 | COIL 1 | — | W19 | — | 0.5 | OEM-3-G | — | — | — |
| 33 | INJECTOR 3 | — | W23 | — | 0.5 | OEM-3-Y | — | — | — |
| 35 | USB D+ | — | — | — | — | — | — | — | — |
| 36 | USB D- | — | — | — | — | — | — | — | — |
| 37 | LOW SIDE RELAY 11 | — | — | — | — | — | — | — | — |
| 38 | USB VBUS | — | — | — | — | — | — | — | — |
| 39 | LOW SIDE 6 | — | W31 | — | 0.5 | OEM-3-O | — | — | — |
| 4 | INJECTOR 2 | — | W22 | — | 0.5 | OEM-3-X | — | — | — |
| 41 | USB GROUND | — | — | — | — | — | — | — | — |
| 42 | LOW SIDE RELAY 12 | — | — | — | — | — | — | — | — |
| 43 | LOW SIDE RELAY 14 | — | — | — | — | — | — | — | — |
| 44 | LOW SIDE 4 | — | W28 | — | 0.5 | OEM-3-N | — | — | — |
| 45 | 5V REF | — | W15 | — | 0.5 | OEM-2-I | — | — | — |
| 46 | 5V REF | — | — | — | — | — | — | — | — |
| 49 | LSU IA | — | — | — | — | — | — | — | — |
| 50 | LSU IP | — | — | — | — | — | — | — | — |
| 51 | CAN 1 LOW | — | — | — | — | — | — | — | — |
| 52 | SENSORS GROUND | — | W13 | — | 0.5 | SP-0V-1 | — | — | — |
| 53 | KNOCK 1 SIGNAL | — | W18 | — | 0.5 | OEM-2-F | — | — | — |
| 55 | SERIAL 1 RX | — | — | — | — | — | — | — | — |
| 56 | ANA VOLT 2 | — | W38 | — | 0.5 | OEM-3-S | — | — | — |
| 57 | ANA TEMP 2 | — | W42 | — | 0.5 | OEM-2-B | — | — | — |
| 6 | DIG_IN 1 | — | W43 | — | 0.5 | OEM-2-D | — | — | — |
| 61 | GROUND | — | W9 | — | 0.85 | SP-GND-1 | — | — | — |
| 63 | INJECTOR 1 | — | W21 | — | 0.5 | OEM-3-W | — | — | — |
| 64 | VBAT | — | W4 | — | 0.85 | SP-14V-1 | — | — | — |
| 67 | Stepper 1 / A1 | — | W32 | — | 0.5 | OEM-1-E | — | — | — |
| 68 | Stepper 2 / A2 | — | W33 | — | 0.5 | OEM-1-O | — | — | — |
| 69 | LOW SIDE 5 | — | W30 | — | 0.5 | OEM-3-V | — | — | — |
| 7 | DIG_IN 2 | — | W44 | — | 0.5 | OEM-1-F | — | — | — |
| 70 | Stepper 3 / B1 | — | W34 | — | 0.5 | OEM-1-Q | — | — | — |
| 71 | Stepper 4 / B2 | — | W35 | — | 0.5 | OEM-2-M | — | — | — |
| 72 | LOW SIDE RELAY 13 | — | — | — | — | — | — | — | — |
| 73 | LOW SIDE 1 | — | W25 | — | 0.5 | OEM-1-I | — | — | — |
| 74 | LOW SIDE 3 | — | W27 | — | 0.5 | OEM-1-S | — | — | — |
| 76 | 5V REF | — | — | — | — | — | — | — | — |
| 79 | TACHOMETER | — | W36 | — | 0.5 | OEM-2-K | — | — | — |
| 80 | CRANK VR- | — | — | — | — | — | — | — | — |
| 81 | CRANK VR+ | — | W16 | — | 0.5 | OEM-2-J | — | — | — |
| 84 | Sensor Ground | — | W14 | — | 0.5 | SP-0V-1 | — | — | — |
| 86 | ANA TEMP 1 | — | W41 | — | 0.5 | OEM-2-E | — | — | — |
| 89 | GROUND | — | W10 | — | 0.85 | SP-GND-1 | — | — | — |
| 90 | GROUND | — | W11 | — | 0.85 | SP-GND-1 | — | — | — |
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 | — | — | — |
| E | Malfunction indicator lamp (MIL) | — | W32 | — | 0.5 | ME221-C1-67 | — | — | — |
| F | Brake switch | — | W44 | — | 0.5 | ME221-C1-7 | — | — | — |
| G | Power steering pressure switch | — | — | — | — | — | — | — | — |
| I | Condenser fan relay | — | W25 | — | 0.5 | ME221-C1-73 | — | — | — |
| O | Alternator control | — | W33 | — | 0.5 | ME221-C1-68 | — | — | — |
| P | A/C request | — | — | — | — | — | — | — | — |
| Q | Charge lamp | — | W34 | — | 0.5 | ME221-C1-70 | — | — | — |
| R | Cooling fan relay | — | W26 | — | 0.5 | ME221-C1-12 | — | — | — |
| S | A/C clutch relay | — | W27 | — | 0.5 | ME221-C1-74 | — | — | — |
| U | Front O2 heater | — | W29 | — | 0.5 | ME221-C1-16 | — | — | — |
| V | Neutral switch | — | — | — | — | — | — | — | — |
OEM-2
| Cavity | Function | Signal | Wire | Colour | Gauge (mm²) | Destination | Terminal | Seal | Plug |
|---|---|---|---|---|---|---|---|---|---|
| A | Fuel tank pressure | — | — | — | — | — | — | — | — |
| B | Intake air temperature (IAT) | — | W42 | — | 0.5 | ME221-C1-57 | — | — | — |
| C | Front O2 signal | — | W40 | — | 0.5 | ME221-C1-18 | — | — | — |
| D | Vehicle speed | — | W43 | — | 0.5 | ME221-C1-6 | — | — | — |
| E | Coolant temperature (ECT) | — | W41 | — | 0.5 | ME221-C1-86 | — | — | — |
| F | Knock sensor | — | W18 | — | 0.5 | ME221-C1-53 | — | — | — |
| H | Cam position (CMP) | — | W17 | — | 0.5 | ME221-C1-22 | — | — | — |
| I | +5V sensor supply | — | W15 | — | 0.5 | ME221-C1-45 | — | — | — |
| J | Crank position (CKP) | — | W16 | — | 0.5 | ME221-C1-81 | — | — | — |
| K | Tachometer output | — | W36 | — | 0.5 | ME221-C1-79 | — | — | — |
| L | Mass air flow (MAF) | — | W37 | — | 0.5 | ME221-C1-26 | — | — | — |
| M | EGR valve | — | W35 | — | 0.5 | ME221-C1-71 | — | — | — |
| N | EGR valve | — | — | — | — | — | — | — | — |
| O | EGR valve | — | — | — | — | — | — | — | — |
| P | EGR valve | — | — | — | — | — | — | — | — |
OEM-3
| Cavity | Function | Signal | Wire | Colour | Gauge (mm²) | Destination | Terminal | Seal | Plug |
|---|---|---|---|---|---|---|---|---|---|
| A | Power ground | — | W5 | — | 0.85 | SP-GND-1 | — | — | — |
| B | Power ground | — | W6 | — | 0.85 | SP-GND-1 | — | — | — |
| C | Power ground | — | W7 | — | 0.85 | SP-GND-1 | — | — | — |
| E | Throttle position (TPS) | — | W39 | — | 0.5 | ME221-C1-17 | — | — | — |
| F | Signal ground | — | W12 | — | 0.5 | SP-0V-1 | — | — | — |
| G | Ignition 1 (coils 1+4, wasted spark) | — | W19 | — | 0.5 | ME221-C1-32 | — | — | — |
| H | Ignition 2 (coils 2+3, wasted spark) | — | W20 | — | 0.5 | ME221-C1-31 | — | — | — |
| I | Clutch switch | — | — | — | — | — | — | — | — |
| J | Rear O2 signal | — | — | — | — | — | — | — | — |
| K | Fuel level | — | — | — | — | — | — | — | — |
| L | Evap purge solenoid | — | — | — | — | — | — | — | — |
| M | ISC valve +14V feed | — | W2 | — | 0.85 | SP-14V-1 | — | — | — |
| N | Fuel pump relay | — | W28 | — | 0.5 | ME221-C1-44 | — | — | — |
| O | ISC valve low side | — | W31 | — | 0.5 | ME221-C1-39 | — | — | — |
| Q | VICS solenoid (intake butterflies) | — | — | — | — | — | — | — | — |
| S | Pressure sensor (Mazda: EGR boost sensor) | — | W38 | — | 0.5 | ME221-C1-56 | — | — | — |
| T | EGR boost solenoid | — | — | — | — | — | — | — | — |
| U | Canister drain cut valve (CDCV) | — | — | — | — | — | — | — | — |
| V | Rear O2 heater | — | W30 | — | 0.5 | ME221-C1-69 | — | — | — |
| W | Injector 1 | — | W21 | — | 0.5 | ME221-C1-63 | — | — | — |
| X | Injector 2 | — | W22 | — | 0.5 | ME221-C1-4 | — | — | — |
| Y | Injector 3 | — | W23 | — | 0.5 | ME221-C1-33 | — | — | — |
| Z | Injector 4 | — | W24 | — | 0.5 | ME221-C1-3 | — | — | — |
SP-0V
| Cavity | Function | Signal | Wire | Colour | Gauge (mm²) | Destination | Terminal | Seal | Plug |
|---|---|---|---|---|---|---|---|---|---|
| 1 | — | — | W12 | — | 0.5 | OEM-3-F | — | — | — |
| 1 | — | — | W13 | — | 0.5 | ME221-C1-52 | — | — | — |
| 1 | — | — | W14 | — | 0.5 | ME221-C1-84 | — | — | — |
SP-14V
| Cavity | Function | Signal | Wire | Colour | Gauge (mm²) | Destination | Terminal | Seal | Plug |
|---|---|---|---|---|---|---|---|---|---|
| 1 | — | — | W1 | — | 0.85 | OEM-1-B | — | — | — |
| 1 | — | — | W2 | — | 0.85 | OEM-3-M | — | — | — |
| 1 | — | — | W3 | — | 0.85 | ME221-C1-15 | — | — | — |
| 1 | — | — | W4 | — | 0.85 | ME221-C1-64 | — | — | — |
SP-GND
| Cavity | Function | Signal | Wire | Colour | Gauge (mm²) | Destination | Terminal | Seal | Plug |
|---|---|---|---|---|---|---|---|---|---|
| 1 | — | — | W5 | — | 0.85 | OEM-3-A | — | — | — |
| 1 | — | — | W6 | — | 0.85 | OEM-3-B | — | — | — |
| 1 | — | — | W7 | — | 0.85 | OEM-3-C | — | — | — |
| 1 | — | — | W8 | — | 0.85 | ME221-C1-10 | — | — | — |
| 1 | — | — | W9 | — | 0.85 | ME221-C1-61 | — | — | — |
| 1 | — | — | W10 | — | 0.85 | ME221-C1-89 | — | — | — |
| 1 | — | — | W11 | — | 0.85 | ME221-C1-90 | — | — | — |
Pin map
| OEM point | OEM function | OEM family | Target point | Target function | Target family | Wire colour | Evidence |
|---|---|---|---|---|---|---|---|
| OEM-1-A | Constant +12V | power_in | — | — | — | single_source | |
| OEM-1-B | ECU power +14V (main relay) | power_in | ME221-C1-15 + ME221-C1-64 | IGN +12V + VBAT | power_in | single_source | |
| OEM-1-E | Malfunction indicator lamp (MIL) | low_side_out | ME221-C1-67 | Stepper 1 / A1 | hbridge_out | single_source | |
| OEM-1-F | Brake switch | digital_in | ME221-C1-7 | DIG_IN 2 | digital_in | single_source | |
| OEM-1-G | Power steering pressure switch | digital_in | — | — | — | single_source | |
| OEM-1-I | Condenser fan relay | low_side_out | ME221-C1-73 | LOW SIDE 1 | low_side_out | single_source | |
| OEM-1-O | Alternator control | low_side_out | ME221-C1-68 | Stepper 2 / A2 | hbridge_out | single_source | |
| OEM-1-P | A/C request | digital_in | — | — | — | single_source | |
| OEM-1-Q | Charge lamp | low_side_out | ME221-C1-70 | Stepper 3 / B1 | hbridge_out | single_source | |
| OEM-1-R | Cooling fan relay | low_side_out | ME221-C1-12 | LOW SIDE 2 | low_side_out | single_source | |
| OEM-1-S | A/C clutch relay | low_side_out | ME221-C1-74 | LOW SIDE 3 | low_side_out | single_source | |
| OEM-1-U | Front O2 heater | low_side_out | ME221-C1-16 | LSU HEATER -VE | low_side_out | single_source | |
| OEM-1-V | Neutral switch | digital_in | — | — | — | single_source | |
| OEM-2-A | Fuel tank pressure | analog_in | — | — | — | single_source | |
| OEM-2-B | Intake air temperature (IAT) | temp_in | ME221-C1-57 | ANA TEMP 2 | temp_in | single_source | |
| OEM-2-C | Front O2 signal | lambda_nb_in | ME221-C1-18 | ANA VOLT 4 | analog_in | single_source | |
| OEM-2-D | Vehicle speed | digital_in | ME221-C1-6 | DIG_IN 1 | digital_in | single_source | |
| OEM-2-E | Coolant temperature (ECT) | temp_in | ME221-C1-86 | ANA TEMP 1 | temp_in | single_source | |
| OEM-2-F | Knock sensor | knock_in | ME221-C1-53 | KNOCK 1 SIGNAL | knock_in | single_source | |
| OEM-2-H | Cam position (CMP) | trigger_in | ME221-C1-22 | CAM A VR+ | trigger_in | single_source | |
| OEM-2-I | +5V sensor supply | vref | ME221-C1-45 | 5V REF | vref | single_source | |
| OEM-2-J | Crank position (CKP) | trigger_in | ME221-C1-81 | CRANK VR+ | trigger_in | single_source | |
| OEM-2-K | Tachometer output | tacho_out | ME221-C1-79 | TACHOMETER | tacho_out | single_source | |
| OEM-2-L | Mass air flow (MAF) | analog_in | ME221-C1-26 | ANA VOLT 1 | analog_in | single_source | |
| OEM-2-M | EGR valve | low_side_out | ME221-C1-71 | Stepper 4 / B2 | hbridge_out | single_source | |
| OEM-2-N | EGR valve | low_side_out | — | — | — | single_source | |
| OEM-2-O | EGR valve | low_side_out | — | — | — | single_source | |
| OEM-2-P | EGR valve | low_side_out | — | — | — | single_source | |
| OEM-3-A | Power ground | ground | ME221-C1-10 + ME221-C1-61 + ME221-C1-89 + ME221-C1-90 | GROUND CHASSIS + GROUND + GROUND + GROUND | ground | single_source | |
| OEM-3-B | Power ground | ground | ME221-C1-10 + ME221-C1-61 + ME221-C1-89 + ME221-C1-90 | GROUND CHASSIS + GROUND + GROUND + GROUND | ground | single_source | |
| OEM-3-C | Power ground | ground | ME221-C1-10 + ME221-C1-61 + ME221-C1-89 + ME221-C1-90 | GROUND CHASSIS + GROUND + GROUND + GROUND | ground | single_source | |
| OEM-3-E | Throttle position (TPS) | analog_in | ME221-C1-17 | ANA VOLT 3 | analog_in | single_source | |
| OEM-3-F | Signal ground | sensor_ground | ME221-C1-52 + ME221-C1-84 | SENSORS GROUND + Sensor Ground | sensor_ground | single_source | |
| OEM-3-G | Ignition 1 (coils 1+4, wasted spark) | ignition_out | ME221-C1-32 | COIL 1 | ignition_out | single_source | |
| OEM-3-H | Ignition 2 (coils 2+3, wasted spark) | ignition_out | ME221-C1-31 | COIL 2 | ignition_out | single_source | |
| OEM-3-I | Clutch switch | digital_in | — | — | — | single_source | |
| OEM-3-J | Rear O2 signal | lambda_nb_in | — | — | — | single_source | |
| OEM-3-K | Fuel level | analog_in | — | — | — | single_source | |
| OEM-3-L | Evap purge solenoid | low_side_out | — | — | — | single_source | |
| OEM-3-M | ISC valve +14V feed | power_in | ME221-C1-15 + ME221-C1-64 | IGN +12V + VBAT | power_in | single_source | |
| OEM-3-N | Fuel pump relay | low_side_out | ME221-C1-44 | LOW SIDE 4 | low_side_out | single_source | |
| OEM-3-O | ISC valve low side | low_side_out | ME221-C1-39 | LOW SIDE 6 | low_side_out | single_source | |
| OEM-3-Q | VICS solenoid (intake butterflies) | low_side_out | — | — | — | single_source | |
| OEM-3-S | Pressure sensor (Mazda: EGR boost sensor) | analog_in | ME221-C1-56 | ANA VOLT 2 | analog_in | single_source | |
| OEM-3-T | EGR boost solenoid | — | — | — | — | single_source | |
| OEM-3-U | Canister drain cut valve (CDCV) | low_side_out | — | — | — | single_source | |
| OEM-3-V | Rear O2 heater | low_side_out | ME221-C1-69 | LOW SIDE 5 | low_side_out | single_source | |
| OEM-3-W | Injector 1 | injector_out | ME221-C1-63 | INJECTOR 1 | injector_out | single_source | |
| OEM-3-X | Injector 2 | injector_out | ME221-C1-4 | INJECTOR 2 | injector_out | single_source | |
| OEM-3-Y | Injector 3 | injector_out | ME221-C1-33 | INJECTOR 3 | injector_out | single_source | |
| OEM-3-Z | Injector 4 | injector_out | ME221-C1-3 | INJECTOR 4 | injector_out | 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 | OEM-3-M | SP-14V-1 | 0.85 | no route | ISC valve +14V feed | — | |
| W3 | SP-14V-1 | ME221-C1-15 | 0.85 | no route | IGN +12V | — | |
| W4 | SP-14V-1 | ME221-C1-64 | 0.85 | no route | VBAT | — | |
| W5 | OEM-3-A | SP-GND-1 | 0.85 | no route | Power ground | — | |
| W6 | OEM-3-B | SP-GND-1 | 0.85 | no route | Power ground | — | |
| W7 | OEM-3-C | SP-GND-1 | 0.85 | no route | Power ground | — | |
| W8 | SP-GND-1 | ME221-C1-10 | 0.85 | no route | GROUND CHASSIS | — | |
| W9 | SP-GND-1 | ME221-C1-61 | 0.85 | no route | GROUND | — | |
| W10 | SP-GND-1 | ME221-C1-89 | 0.85 | no route | GROUND | — | |
| W11 | SP-GND-1 | ME221-C1-90 | 0.85 | no route | GROUND | — | |
| W12 | OEM-3-F | SP-0V-1 | 0.5 | no route | Signal ground | — | |
| W13 | SP-0V-1 | ME221-C1-52 | 0.5 | no route | SENSORS GROUND | — | |
| W14 | SP-0V-1 | ME221-C1-84 | 0.5 | no route | Sensor Ground | — | |
| W15 | OEM-2-I | ME221-C1-45 | 0.5 | no route | +5V sensor supply | — | |
| W16 | OEM-2-J | ME221-C1-81 | 0.5 | no route | Crank position (CKP) | — | |
| W17 | OEM-2-H | ME221-C1-22 | 0.5 | no route | Cam position (CMP) | — | |
| W18 | OEM-2-F | ME221-C1-53 | 0.5 | no route | Knock sensor | — | |
| W19 | OEM-3-G | ME221-C1-32 | 0.5 | no route | Ignition 1 (coils 1+4, wasted spark) | — | |
| W20 | OEM-3-H | ME221-C1-31 | 0.5 | no route | Ignition 2 (coils 2+3, wasted spark) | — | |
| W21 | OEM-3-W | ME221-C1-63 | 0.5 | no route | Injector 1 | — | |
| W22 | OEM-3-X | ME221-C1-4 | 0.5 | no route | Injector 2 | — | |
| W23 | OEM-3-Y | ME221-C1-33 | 0.5 | no route | Injector 3 | — | |
| W24 | OEM-3-Z | ME221-C1-3 | 0.5 | no route | Injector 4 | — | |
| W25 | OEM-1-I | ME221-C1-73 | 0.5 | no route | Condenser fan relay | — | |
| W26 | OEM-1-R | ME221-C1-12 | 0.5 | no route | Cooling fan relay | — | |
| W27 | OEM-1-S | ME221-C1-74 | 0.5 | no route | A/C clutch relay | — | |
| W28 | OEM-3-N | ME221-C1-44 | 0.5 | no route | Fuel pump relay | — | |
| W29 | OEM-1-U | ME221-C1-16 | 0.5 | no route | Front O2 heater | — | |
| W30 | OEM-3-V | ME221-C1-69 | 0.5 | no route | Rear O2 heater | — | |
| W31 | OEM-3-O | ME221-C1-39 | 0.5 | no route | ISC valve low side | — | |
| W32 | OEM-1-E | ME221-C1-67 | 0.5 | no route | Malfunction indicator lamp (MIL) | — | |
| W33 | OEM-1-O | ME221-C1-68 | 0.5 | no route | Alternator control | — | |
| W34 | OEM-1-Q | ME221-C1-70 | 0.5 | no route | Charge lamp | — | |
| W35 | OEM-2-M | ME221-C1-71 | 0.5 | no route | EGR valve | — | |
| W36 | OEM-2-K | ME221-C1-79 | 0.5 | no route | Tachometer output | — | |
| W37 | OEM-2-L | ME221-C1-26 | 0.5 | no route | Mass air flow (MAF) | — | |
| W38 | OEM-3-S | ME221-C1-56 | 0.5 | no route | Pressure sensor (Mazda: EGR boost sensor) | — | |
| W39 | OEM-3-E | ME221-C1-17 | 0.5 | no route | Throttle position (TPS) | — | |
| W40 | OEM-2-C | ME221-C1-18 | 0.5 | no route | Front O2 signal | — | |
| W41 | OEM-2-E | ME221-C1-86 | 0.5 | no route | Coolant temperature (ECT) | — | |
| W42 | OEM-2-B | ME221-C1-57 | 0.5 | no route | Intake air temperature (IAT) | — | |
| W43 | OEM-2-D | ME221-C1-6 | 0.5 | no route | Vehicle speed | — | |
| W44 | OEM-1-F | ME221-C1-7 | 0.5 | no route | Brake switch | — |
Bill of materials
| Category | Part number | Manufacturer | Description | Qty | Unit |
|---|---|---|---|---|---|
| connector | 174514-6 | TE | AMP Multilock .040/.070 hybrid 16-pin female harness plug (Miata NB1 ECU) | 1.000 | ea |
| 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 (5)
| Severity | Code | Subject | Message |
|---|---|---|---|
| warn | NET_FAMILY | OEM-1-E ↔ ME221-C1-67 | OEM-1-E "Malfunction indicator lamp (MIL)" [low_side_out] is wired to ME221-C1-67 "Stepper 1 / A1" [hbridge_out]. A half-bridge can act as a low-side switch only if configured that way. |
| warn | NET_FAMILY | OEM-1-O ↔ ME221-C1-68 | OEM-1-O "Alternator control" [low_side_out] is wired to ME221-C1-68 "Stepper 2 / A2" [hbridge_out]. A half-bridge can act as a low-side switch only if configured that way. |
| warn | NET_FAMILY | OEM-1-Q ↔ ME221-C1-70 | OEM-1-Q "Charge lamp" [low_side_out] is wired to ME221-C1-70 "Stepper 3 / B1" [hbridge_out]. A half-bridge can act as a low-side switch only if configured that way. |
| warn | NET_FAMILY | OEM-2-M ↔ ME221-C1-71 | OEM-2-M "EGR valve" [low_side_out] is wired to ME221-C1-71 "Stepper 4 / B2" [hbridge_out]. A half-bridge can act as a low-side switch only if configured that way. |
| info | UNMAPPED | OEM | 14 optional OEM pins are not mapped: OEM-1-G Power steering pressure switch; OEM-1-P A/C request; OEM-1-V Neutral switch; OEM-2-A Fuel tank pressure; OEM-2-N EGR valve; OEM-2-O EGR valve; OEM-2-P EGR valve; OEM-3-I Clutch switch; OEM-3-J Rear O2 signal; OEM-3-K Fuel level; OEM-3-L Evap purge solenoid; OEM-3-Q VICS solenoid (intake butterflies); OEM-3-T EGR boost solenoid; OEM-3-U Canister drain cut valve (CDCV) |
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 2026-10-09. Review every wire against both manuals before building. Not wired: - OEM-1 A: Constant +12V: Motorsport Electronics ME221 has no battery-constant input; not needed - OEM-2 N: EGR valve: no free low_side/ls_hs/injector/hbridge on Motorsport Electronics ME221 - OEM-2 O: EGR valve: no free low_side/ls_hs/injector/hbridge on Motorsport Electronics ME221 - OEM-2 P: EGR valve: no free low_side/ls_hs/injector/hbridge on Motorsport Electronics ME221 - OEM-3 L: Evap purge solenoid: no free low_side/ls_hs/injector/hbridge on Motorsport Electronics ME221 - OEM-3 Q: VICS solenoid (intake butterflies): no free low_side/ls_hs/injector/hbridge on Motorsport Electronics ME221 - OEM-3 U: Canister drain cut valve (CDCV): no free low_side/ls_hs/injector/hbridge on Motorsport Electronics ME221 - OEM-3 J: Rear O2 signal: no free o2_narrowband/analog_0_5 on Motorsport Electronics ME221 - OEM-2 A: Fuel tank pressure: no free analog_0_5 on Motorsport Electronics ME221 - OEM-3 K: Fuel level: no free analog_0_5 on Motorsport Electronics ME221 - OEM-1 G: Power steering pressure switch: no free switch_in/frequency_in/analog_0_5 on Motorsport Electronics ME221 - OEM-1 P: A/C request: no free switch_in/frequency_in/analog_0_5 on Motorsport Electronics ME221 - OEM-1 V: Neutral switch: no free switch_in/frequency_in/analog_0_5 on Motorsport Electronics ME221 - OEM-3 I: Clutch switch: no free switch_in/frequency_in/analog_0_5 on Motorsport Electronics ME221 - OEM-3 T: EGR boost solenoid: not classified in the library; wire by hand
Sources
| Reliability | Kind | Title | URL | Archive | Captured | SHA-256 |
|---|---|---|---|---|---|---|
| 4 | vendor_doc | Link G4X MX5NB1X install manual (NB1 1999-00) | https://linkecu.com/documentation/MX5XNB1.pdf | archive | 2026-10-05 | 2e36c91270cc |
| 4 | vendor_doc | Motorsport Electronics GEN2 ME221/ME360/ME442 wire-in pinout | https://motorsport-electronics.co.uk/onlinehelp/html/ME442ME360ME221GEN2Wire-InPinout.html | — | — | — |
| 2 | expert_report | Justin Barrera — Miata NA/NB wiring corrections | — | — | — | — |