Connector A is generally responsible for the high-current devices and the main power supply of the ECU.

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| Pin | Function | Signal Type | Wire Color (Typical Fiat) | Notes | | :--- | :--- | :--- | :--- | :--- | | | Injector 4 (Cylinder 4) | Output, Ground-switched | Grey/Blue | Saturated driver (12V peak/hold) | | 2 | Injector 3 (Cylinder 3) | Output, Ground-switched | Yellow/Blue | | | 3 | Main Relay Control | Output, +12V enable | Blue/Black | Powers ECU +12V from battery | | 4 | | | | | | 5 | +12V Battery Backup | Power Input | Red/White | Permanent +12V from battery | | 6 | | | | | | 7 | Injector 2 (Cylinder 2) | Output, Ground-switched | Green/Blue | | | 8 | Injector 1 (Cylinder 1) | Output, Ground-switched | Red/Blue | | | 9 | Chassis Ground (Power) | Ground | Black/White | Heavy gauge wire | | 10 | Chassis Ground (Power) | Ground | Black/White | Second heavy gauge wire | | 11 | Ignition Coil 2 & 3 (Wasted spark) | Output, 5V logic | White/Black | Triggers external ignition module (e.g., Bosch 227) | | 12 | Ignition Coil 1 & 4 (Wasted spark) | Output, 5V logic | White/Green | Triggers external ignition module | | 13 | | | | | | 14 | Engine Ground (Sensor return) | Sensor Ground | Brown/White | Must remain clean; do not mix with power ground | | 15 | +5V Sensor Reference | Output | Red/Black | Supplies TPS, MAP, CTS, IAT | | 16 | EGO Heater Ground (Lambda) | Output, Ground-switched | Green/White | Oxygen sensor heater control | | 17 | | | | | | 18 | | | | | | 19 | Diagnostic K-Line (ISO 9141) | Bidirectional | Yellow/Black | OBD-II pin 7 of DLC | | 20 | Fuel Pump Relay | Output, Ground-switched | Red/Yellow | Energizes relay to run fuel pump | | 21 | RPM Output (to dashboard) | Output, 12V square wave | White | Tachometer signal | | 22 | Idle Air Control (IAC) - Coil A | Output, PWM | Orange/White | Stepper motor or PWM valve | | 23 | Idle Air Control (IAC) - Coil B | Output, PWM | Orange/Black | | | 24 | VVT Solenoid (Alfa Romeo Variants) | Output, Ground-switched | White/Purple | Variable valve timing control | | 25 | CAN Low (OBD-II) (Late models) | Bidirectional | Green/Brown | Not used on early 48P2 | | 26 | CAN High (OBD-II) (Late models) | Bidirectional | Purple/Brown | Not used on early 48P2 | | 27 | | | | | | 28 | Vehicle Speed Sensor (VSS) | Input, digital | Purple/White | From gearbox sensor or ABS | | 29 | EGO Sensor (Lambda) | Input, 0-1V (Narrowband) | Black/White | Zirconia sensor signal | | 30 | Engine Coolant Temp (CTS) | Input, Analog | Light Blue/Violet | NTC thermistor (2.5kΩ @ 20°C) | | 31 | Intake Air Temp (IAT) | Input, Analog | Grey/Red | NTC sensor in airbox/MAF | | 32 | Throttle Position Sensor (TPS) | Input, Analog | Blue/White | 0-5V potentiometer | | 33 | | | | | | 34 | Crankshaft Position Sensor (+) | Input, VR differential | Red/Black | From 60-2 tooth wheel on flywheel | | 35 | Crankshaft Position Sensor (-) | Input, VR differential | Red/White | Shielded twisted pair | | 36 | Camshaft Position Sensor (Phase) | Input, Hall effect | Yellow/White | TDC cylinder 1 detection | | 37 | | | | | | 38 | Air Conditioning Request | Input, +12V | Blue/Green | From A/C panel | | 39 | Power Steering Pressure Switch | Input, Ground trigger | Purple/Black | Raises idle when turning | | 40 | Brake Light Switch | Input, +12V | White/Red | TCS / deceleration fuel cut | | 41 | Knock Sensor | Input, AC signal | Coaxial cable | Piezoelectric sensor (shielded) | | 42 | MAP Sensor (Internal) | Input, Analog | N/A - Inside ECU | Reads manifold vacuum via hose | | 43 | | | | | | 44 | OBD-II K-Line (alternative) | Bidirectional | Yellow/White | Secondary diagnostic line | | 45 | Main Relay Feedback | Input, +12V | Black/White | Verifies relay is energized | | 46 | +12V Switched (Ignition) | Power Input | Blue/Red | 12V from ignition key (run/crank) | | 47 | | | | | | 48 | | | | |

Always disconnect the battery negative terminal before probing the ECU connector. Never back-probe a sealed connector with a steel needle; use proper breakout leads.