While physical plug designs changed across generations, Toyota has maintained consistent acronyms for terminal functions for decades. When looking at a factory wiring diagram, these are the primary pins you will encounter: Power and Ground Terminals : Main switched +12V power from the EFI relay.
: 5V reference voltage output for sensors like the TPS.
Example: 89661 - 3A490 │ │ ECU Prefix Unique Model & Market Code
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: A 5V reference output sent to power sensors like the Throttle Position Sensor (TPS). IGT (1, 2, 3...)
: Ignition Trigger signal sent from the ECU to the igniter/coil to fire the spark plug.
These ECUs typically use 26-pin, 16-pin, or 22-pin connectors. Example: 89661 - 3A490 │ │ ECU Prefix
Never splice sensor grounds ( E2 ) into chassis grounds ( E1 ). Doing so introduces electrical noise into sensitive voltage loops, causing erratic idle, ghost fault codes, and poor drivability.
Look for online forums like PlanetSoarer or specific Toyota swap groups on Facebook, which often hold PDF pinouts for popular engines.
: Know the exact engine stamp (e.g., 1NZ-FE, 7M-GE). These ECUs typically use 26-pin, 16-pin, or 22-pin
This earlier 4A-GE ECU uses a different labeling scheme, but many core functions share the same or similar pin names.
Ignition Trigger signals sent from the ECU to the igniter or coil-on-plug units to dictate spark timing.
: Wire IGSW , +B , and +B1 together. Connect them to the positive 12V supply through a toggle switch. This switch acts as your ignition key.
89661 is a part number prefix , not a specific model code. Toyota used this prefix on dozens of ECUs with different plug shapes, pin counts, and pin functions. You must confirm your exact ECU ID (e.g., 89661-12345 ) and vehicle model/year.