First of all. This is VERY not silly. This is why the forum exists. Rest assured, you're in the right place.
Secondly. I have not troubleshot many of these and they are sort of weird complex puzzles to service. But I AM certified to repair them (take that for what you will Apple repair certifications don't mean much).
The verbiage from the repair manual for this model specifically says:
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[quote]#8: PCIe Switch Status: This indicates the status of the link from the PCIe switch on the I/O Board to the CPU. During
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[quote]
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#8: PCIe Switch Status: This indicates the status of the link from the PCIe switch on the I/O Board to the CPU. During startup, this indicates that the system has reached EFI Boot. If the link to the PCIe switch is not operating in PCIe v3 mode, this LED will blink. A fast blink indicates v2 mode, while a slow blink indicates v1 mode. These states may correlate to issues with Thunderbolt or USB devices.
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startup, this indicates that the system has reached EFI Boot. If the link to the PCIe switch is not operating in PCIe v3
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mode, this LED will blink. A fast blink indicates v2 mode, while a slow blink indicates v1 mode. These states may
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correlate to issues with Thunderbolt or USB devices.[/quote]
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[/quote]
So it sounds to me like you're in the right neighborhood. It's attempting to boot, but could be an issue with either thunderbolt or USB devices. So could be something wrong with a specific peripheral, the IO board itself, the IO board flex cable connector or a bunch of other things further down the rabbit hole. I might also check [document|27523|the Repair Manual for this model] since it will have some specific troubleshooting flows you can use.
First of all. This is VERY not silly. This is why the forum exists. Rest assured, you're in the right place.
Secondly. I have not troubleshot many of these and they are sort of weird complex puzzles to service. But I AM certified to repair them (take that for what you will Apple repair certifications don't mean much).
The verbiage from the repair manual for this model specifically says:
[quote]#8: PCIe Switch Status: This indicates the status of the link from the PCIe switch on the I/O Board to the CPU. During
startup, this indicates that the system has reached EFI Boot. If the link to the PCIe switch is not operating in PCIe v3
mode, this LED will blink. A fast blink indicates v2 mode, while a slow blink indicates v1 mode. These states may
correlate to issues with Thunderbolt or USB devices.[/quote]
So it sounds to me like you're in the right neighborhood. It's attempting to boot, but could be an issue with either thunderbolt or USB devices. So could be something wrong with a specific peripheral, the IO board itself, the IO board flex cable connector or a bunch of other things further down the rabbit hole. I might also check [document|27523|the Repair Manual for this model] since it will have some specific troubleshooting flows you can use.