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MX-5 Miata NA8 1994-97 (BP-ZE, 1.8) → Haltech Nexus S3 HT-213000 (auto)

MX-5 Miata NA8 1994-97 (BP-ZE, 1.8) — Haltech — Nexus S3
Drawn by Michael Gnankou · Rev 0 · proposal · 2026-10-05

Revisions

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Schematic

NEXUSS3-ANEXUSS3-COEM-1OEM-2SP-0VSP-14VSP-GND

Connectors

NEXUSS3-A

CavityFunctionSignalWireColourGauge (mm²)DestinationTerminalSealPlug
1Injector 1—W19—0.5OEM-2-U———
10Battery ground—W8—0.85SP-GND-1———
11Battery ground—W9—0.85SP-GND-1———
12DPO 2—W25—0.5OEM-2-S———
13Ignition switch input————————
14DPO 3—W26—0.5OEM-2-T———
15DPO 4—W27—0.5OEM-2-W———
16DPO 5—W28—0.5OEM-1-E———
17DPO 6—W29—0.5OEM-2-R———
18+12V switched input—W2—0.85SP-14V-1———
19HBO 1————————
2Injector 2—W20—0.5OEM-2-V———
20HBO 2————————
21HBO 3————————
22HBO 4————————
23CAN 1 High————————
24CAN 1 Low————————
25+12V switched input—W3—0.85SP-14V-1———
26ECR output—W23—0.5OEM-1-J———
27Ignition 1—W17—0.5OEM-1-G———
28Ignition 2—W18—0.5OEM-1-H———
29Ignition 3————————
3Injector 3—W21—0.5OEM-2-Y———
30Ignition 4————————
31Ignition 5————————
32Ignition 6————————
33Ignition 7————————
34Ignition 8————————
4Injector 4—W22—0.5OEM-2-Z———
5Injector 5—W30—0.5OEM-2-X———
6Injector 6————————
7Injector 7————————
8Injector 8————————
9DPO 1—W24—0.5OEM-1-R———

NEXUSS3-C

CavityFunctionSignalWireColourGauge (mm²)DestinationTerminalSealPlug
1Trigger +—W13—0.5OEM-2-E———
10AVI 1—W31—0.5OEM-2-O———
11AVI 2—W32—0.5OEM-2-M———
12AVI 3—W33—0.5OEM-2-N———
13AVI 4—W34—0.5OEM-2-Q———
14AVI 5—W35—0.5OEM-2-P———
15AVI 6————————
16AVI 7————————
17AVI 8————————
18AVI 9————————
19SPI 5—W40—0.5OEM-1-V———
2Trigger -—W14—0.5SP-0V-1———
20SPI 6————————
21CAN 2 High————————
22CAN 2 Low————————
23Knock 1————————
24Knock 2————————
25+5V—W12—0.5OEM-2-K———
26Signal ground—W11—0.5SP-0V-1———
27AVI 10————————
28AVI 11————————
29WBI 1 Heater +————————
3Home +—W15—0.5OEM-2-G———
30WBI 1 Input————————
31WBI 1 Pump————————
32WBI 1 Nernst————————
33WBI 1 Heater -————————
34WBI 1 Cal————————
4Home -—W16—0.5SP-0V-1———
5SPI 1—W36—0.5OEM-1-M———
6SPI 2—W37—0.5OEM-1-C———
7SPI 3—W38—0.5OEM-1-P———
8SPI 4—W39—0.5OEM-1-Q———
9+8V————————

OEM-1

CavityFunctionSignalWireColourGauge (mm²)DestinationTerminalSealPlug
AConstant +12V————————
BECU power +14V (main relay)—W1—0.85SP-14V-1———
CStart signal—W37—0.5NEXUSS3-C-6———
EMalfunction indicator lamp (MIL)—W28—0.5NEXUSS3-A-16———
GIgnition 1 (coils 1+4, wasted spark)—W17—0.5NEXUSS3-A-27———
HIgnition 2 (coils 2+3, wasted spark)—W18—0.5NEXUSS3-A-28———
JA/C relay—W23—0.5NEXUSS3-A-26———
MVehicle speed—W36—0.5NEXUSS3-C-5———
PPower steering pressure switch—W38—0.5NEXUSS3-C-7———
QA/C request—W39—0.5NEXUSS3-C-8———
RCooling fan relay—W24—0.5NEXUSS3-A-9———
VNeutral/clutch switch—W40—0.5NEXUSS3-C-19———

OEM-2

CavityFunctionSignalWireColourGauge (mm²)DestinationTerminalSealPlug
APower ground—W4—0.85SP-GND-1———
BPower ground—W5—0.85SP-GND-1———
CPower ground—W6—0.85SP-GND-1———
DPower ground—W7—0.85SP-GND-1———
ECrank position (CAS NE)—W13—0.5NEXUSS3-C-1———
FMAF ground—W10—0.5SP-0V-1———
GCam position (CAS G)—W15—0.5NEXUSS3-C-3———
ITachometer output————————
K+5V sensor supply—W12—0.5NEXUSS3-C-25———
MThrottle position (TPS)—W32—0.5NEXUSS3-C-11———
NO2 sensor—W33—0.5NEXUSS3-C-12———
OMass air flow (MAF)—W31—0.5NEXUSS3-C-10———
PIntake air temperature (IAT)—W35—0.5NEXUSS3-C-14———
QCoolant temperature (ECT)—W34—0.5NEXUSS3-C-13———
RPRC solenoid (fuel pressure regulator)—W29—0.5NEXUSS3-A-17———
SCondenser fan relay—W25—0.5NEXUSS3-A-12———
TFuel pump relay—W26—0.5NEXUSS3-A-14———
UInjector 1—W19—0.5NEXUSS3-A-1———
VInjector 2—W20—0.5NEXUSS3-A-2———
WISC solenoid—W27—0.5NEXUSS3-A-15———
XEvap purge solenoid—W30—0.5NEXUSS3-A-5———
YInjector 3—W21—0.5NEXUSS3-A-3———
ZInjector 4—W22—0.5NEXUSS3-A-4———

SP-0V

CavityFunctionSignalWireColourGauge (mm²)DestinationTerminalSealPlug
1——W10—0.5OEM-2-F———
1——W11—0.5NEXUSS3-C-26———
1——W14—0.5NEXUSS3-C-2———
1——W16—0.5NEXUSS3-C-4———

SP-14V

CavityFunctionSignalWireColourGauge (mm²)DestinationTerminalSealPlug
1——W1—0.85OEM-1-B———
1——W2—0.85NEXUSS3-A-18———
1——W3—0.85NEXUSS3-A-25———

SP-GND

CavityFunctionSignalWireColourGauge (mm²)DestinationTerminalSealPlug
1——W4—0.85OEM-2-A———
1——W5—0.85OEM-2-B———
1——W6—0.85OEM-2-C———
1——W7—0.85OEM-2-D———
1——W8—0.85NEXUSS3-A-10———
1——W9—0.85NEXUSS3-A-11———

Pin map

OEM pointOEM functionOEM familyTarget pointTarget functionTarget familyWire colourEvidence
OEM-1-AConstant +12Vpower_in———single_source
OEM-1-BECU power +14V (main relay)power_inNEXUSS3-A-18 + NEXUSS3-A-25+12V switched input + +12V switched inputpower_insingle_source
OEM-1-CStart signaldigital_inNEXUSS3-C-6SPI 2digital_insingle_source
OEM-1-EMalfunction indicator lamp (MIL)low_side_outNEXUSS3-A-16DPO 5low_side_outsingle_source
OEM-1-GIgnition 1 (coils 1+4, wasted spark)ignition_outNEXUSS3-A-27Ignition 1ignition_outsingle_source
OEM-1-HIgnition 2 (coils 2+3, wasted spark)ignition_outNEXUSS3-A-28Ignition 2ignition_outsingle_source
OEM-1-JA/C relaylow_side_outNEXUSS3-A-26ECR outputlow_side_outsingle_source
OEM-1-MVehicle speeddigital_inNEXUSS3-C-5SPI 1digital_insingle_source
OEM-1-PPower steering pressure switchdigital_inNEXUSS3-C-7SPI 3digital_insingle_source
OEM-1-QA/C requestdigital_inNEXUSS3-C-8SPI 4digital_insingle_source
OEM-1-RCooling fan relaylow_side_outNEXUSS3-A-9DPO 1low_side_outsingle_source
OEM-1-VNeutral/clutch switchdigital_inNEXUSS3-C-19SPI 5digital_insingle_source
OEM-2-APower groundgroundNEXUSS3-A-10 + NEXUSS3-A-11Battery ground + Battery groundgroundsingle_source
OEM-2-BPower groundgroundNEXUSS3-A-10 + NEXUSS3-A-11Battery ground + Battery groundgroundsingle_source
OEM-2-CPower groundgroundNEXUSS3-A-10 + NEXUSS3-A-11Battery ground + Battery groundgroundsingle_source
OEM-2-DPower groundgroundNEXUSS3-A-10 + NEXUSS3-A-11Battery ground + Battery groundgroundsingle_source
OEM-2-ECrank position (CAS NE)trigger_inNEXUSS3-C-1Trigger +trigger_insingle_source
OEM-2-FMAF groundsensor_groundNEXUSS3-C-2 + NEXUSS3-C-26 + NEXUSS3-C-4Trigger - + Signal ground + Home -sensor_ground + trigger_insingle_source
OEM-2-GCam position (CAS G)trigger_inNEXUSS3-C-3Home +trigger_insingle_source
OEM-2-ITachometer outputtacho_out———single_source
OEM-2-K+5V sensor supplyvrefNEXUSS3-C-25+5Vvrefsingle_source
OEM-2-MThrottle position (TPS)analog_inNEXUSS3-C-11AVI 2analog_insingle_source
OEM-2-NO2 sensorlambda_nb_inNEXUSS3-C-12AVI 3analog_insingle_source
OEM-2-OMass air flow (MAF)analog_inNEXUSS3-C-10AVI 1analog_insingle_source
OEM-2-PIntake air temperature (IAT)temp_inNEXUSS3-C-14AVI 5analog_insingle_source
OEM-2-QCoolant temperature (ECT)temp_inNEXUSS3-C-13AVI 4analog_insingle_source
OEM-2-RPRC solenoid (fuel pressure regulator)low_side_outNEXUSS3-A-17DPO 6low_side_outsingle_source
OEM-2-SCondenser fan relaylow_side_outNEXUSS3-A-12DPO 2low_side_outsingle_source
OEM-2-TFuel pump relaylow_side_outNEXUSS3-A-14DPO 3low_side_outsingle_source
OEM-2-UInjector 1injector_outNEXUSS3-A-1Injector 1injector_outsingle_source
OEM-2-VInjector 2injector_outNEXUSS3-A-2Injector 2injector_outsingle_source
OEM-2-WISC solenoidlow_side_outNEXUSS3-A-15DPO 4low_side_outsingle_source
OEM-2-XEvap purge solenoidlow_side_outNEXUSS3-A-5Injector 5injector_outsingle_source
OEM-2-YInjector 3injector_outNEXUSS3-A-3Injector 3injector_outsingle_source
OEM-2-ZInjector 4injector_outNEXUSS3-A-4Injector 4injector_outsingle_source

Cut list

WireFromToGauge (mm²)ColourLengthSignalIdent
W1OEM-1-BSP-14V-10.85no routeECU power +14V (main relay)—
W2SP-14V-1NEXUSS3-A-180.85no route+12V switched input—
W3SP-14V-1NEXUSS3-A-250.85no route+12V switched input—
W4OEM-2-ASP-GND-10.85no routePower ground—
W5OEM-2-BSP-GND-10.85no routePower ground—
W6OEM-2-CSP-GND-10.85no routePower ground—
W7OEM-2-DSP-GND-10.85no routePower ground—
W8SP-GND-1NEXUSS3-A-100.85no routeBattery ground—
W9SP-GND-1NEXUSS3-A-110.85no routeBattery ground—
W10OEM-2-FSP-0V-10.5no routeMAF ground—
W11SP-0V-1NEXUSS3-C-260.5no routeSignal ground—
W12OEM-2-KNEXUSS3-C-250.5no route+5V sensor supply—
W13OEM-2-ENEXUSS3-C-10.5no routeCrank position (CAS NE)—
W14SP-0V-1NEXUSS3-C-20.5no routeTrigger -—
W15OEM-2-GNEXUSS3-C-30.5no routeCam position (CAS G)—
W16SP-0V-1NEXUSS3-C-40.5no routeHome -—
W17OEM-1-GNEXUSS3-A-270.5no routeIgnition 1 (coils 1+4, wasted spark)—
W18OEM-1-HNEXUSS3-A-280.5no routeIgnition 2 (coils 2+3, wasted spark)—
W19OEM-2-UNEXUSS3-A-10.5no routeInjector 1—
W20OEM-2-VNEXUSS3-A-20.5no routeInjector 2—
W21OEM-2-YNEXUSS3-A-30.5no routeInjector 3—
W22OEM-2-ZNEXUSS3-A-40.5no routeInjector 4—
W23OEM-1-JNEXUSS3-A-260.5no routeA/C relay—
W24OEM-1-RNEXUSS3-A-90.5no routeCooling fan relay—
W25OEM-2-SNEXUSS3-A-120.5no routeCondenser fan relay—
W26OEM-2-TNEXUSS3-A-140.5no routeFuel pump relay—
W27OEM-2-WNEXUSS3-A-150.5no routeISC solenoid—
W28OEM-1-ENEXUSS3-A-160.5no routeMalfunction indicator lamp (MIL)—
W29OEM-2-RNEXUSS3-A-170.5no routePRC solenoid (fuel pressure regulator)—
W30OEM-2-XNEXUSS3-A-50.5no routeEvap purge solenoid—
W31OEM-2-ONEXUSS3-C-100.5no routeMass air flow (MAF)—
W32OEM-2-MNEXUSS3-C-110.5no routeThrottle position (TPS)—
W33OEM-2-NNEXUSS3-C-120.5no routeO2 sensor—
W34OEM-2-QNEXUSS3-C-130.5no routeCoolant temperature (ECT)—
W35OEM-2-PNEXUSS3-C-140.5no routeIntake air temperature (IAT)—
W36OEM-1-MNEXUSS3-C-50.5no routeVehicle speed—
W37OEM-1-CNEXUSS3-C-60.5no routeStart signal—
W38OEM-1-PNEXUSS3-C-70.5no routePower steering pressure switch—
W39OEM-1-QNEXUSS3-C-80.5no routeA/C request—
W40OEM-1-VNEXUSS3-C-190.5no routeNeutral/clutch switch—

Bill of materials

CategoryPart numberManufacturerDescriptionQtyUnit

ECU setup sheet

RoleEngine refEngine signalSensorECU pointECU functionECU classSetup flag
No configured channels.

Findings

Open (6)

SeverityCodeSubjectMessage
warnLOAD_UNKNOWNNEXUSS3-A-26NEXUSS3-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.
infoNET_FAMILYOEM-2-F ↔ NEXUSS3-C-4OEM-2-F "MAF 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.
infoNET_FAMILYOEM-2-P ↔ NEXUSS3-C-14OEM-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.
infoNET_FAMILYOEM-2-Q ↔ NEXUSS3-C-13OEM-2-Q "Coolant temperature (ECT)" [temp_in] is wired to NEXUSS3-C-13 "AVI 4" [analog_in]. Thermistor on a plain analog input needs a pull-up; check the channel can enable one.
infoNET_FAMILYOEM-2-X ↔ NEXUSS3-A-5OEM-2-X "Evap purge solenoid" [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.
infoUNMAPPEDOEM1 optional OEM pins are not mapped: OEM-2-I Tachometer output

Accepted (1)

CodeSubjectReasonBy
REQUIRED_UNMAPPEDOEM-1-ABattery-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 2026-10-04. 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 - NEXUSS3-A 13: Ignition switch input: not fed (the stock ECU has no ignition-sense pin); feed it from a switched-ignition source

Sources

ReliabilityKindTitleURL
4vendor_docHaltech: Nexus S3 Plug 'n' Play adapter QSG (Subaru WRX/STI ADM, HT-186300) — ECU Connector A & C pinouthttps://www.haltech.com/product/ht-186300-nexus-s3-plug-n-play-adapter-harness/
4vendor_docHaltech: Nexus S3/S2 ECU Overview (QSG) — specificationshttps://store.haltech.com/product/ht-213000-nexus-s3-ecu-only/
4vendor_docLink G4X MX5X install manual (NA 1.6/1.8)https://linkecu.com/documentation/MX5X.pdf