Apple Diagnostic Lights

• Make sure to check Apple Computer Beep Codes for the major diagnostic LEDs and sound/beep codes.

This article is meant to discuss less-known diagnostic lights that Apple provides:

Generic diagnostic lights (for most Apple computers)

• LED lights near the power button: Apple Computer Beep Codes
• Audio (microphone or headphone) jacks have a LED light inside. If this light is red, it means the audio jack is failing or "stuck". Sometimes inserting a headphone in the jack resolves the issue.

Mac Pro

• Has diagnostic lights on the RAM riser cards (where the RAM plugs in). Each RAM stick has a little LED. If the LED remains red after booting, then there may be a problem with that RAM stick or with the RAM slot. (lights shown in the picture on the right =>)

Mac Pro RAM Diagnostic Lights (click for larger version)