J1850 GM Bench harness

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This page documents a commercially-purchased bench flash harness for early GM vehicles. The original intended application was 99-02 F/Y body vehicles using the 12200411 PCM but it may work for others.

OBD2 port:

  • 2: J1850 data (purple)
  • 4: GND (black)
  • 5: GND (black)
  • 16: Unswitched +12V (orange)


ECU port:

  • 19: Switched +12V (pink)
  • 20: Unswitched +12V (orange)
  • 59: J1850 data (purple)
  • 60: GND (black)

PDF of pinouts for 99-02 F/Y body: (http://mrk-motorsports.com/pdf/99-02%20LS1%20PCM%20Pinouts.pdf)

Pictures: (click for full size)

GM 1850 bench flash harness.jpg

OBD2 port GM1850.jpg

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ECM bottom.jpg