Here is the chart on how to read the '''Diagnostic LEDS'''
The Mac Pro (Early 2008) logic board includes a set of LEDs to help service providers troubleshoot the computer. The LEDs are located on the logic board between the two DIMM riser card connectors. LEDs 3, 4, 5, and 6 are normally off and will automatically illuminate if an error occurs. To read LEDs 1, 2, 7, 8, and 9, you must press the DIAG_LED button, which is adjacent to the LEDs. To press the DIAG_LED button, use the nylon probe tool (Apple part number 922-5065).
Use the following table to interpret the LEDs.
https://www.macrepaircentral.us/mac-pro-early-2008/diagnostic-leds.html
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