Before you cut a single wire, spend $20 on a set of ECU terminal extraction tools. Remove the pins one by one and physically trace them to your engine sensors. Write your own pinout chart. Laminate it. Put it in your glovebox.
To avoid frying a processor when probing a Zexel ECU terminal directly: nissan zexel ecu pinout work
Use a fine paperclip or backprobe pins. With the ECU connected and ignition ON (engine off): Before you cut a single wire, spend $20
Verify the ECU is generating the required 5V reference for sensors. Before you cut a single wire
If you are deep into the vintage Nissan game—specifically the S13, R32, Z32, or P10 era—you have likely heard the name muttered in the same breath as "standalone conversion" or "wiring nightmare."