Dell OptiPlex 990 (Early 2011) - Manual (Page 36)

8. Pry the power-switch cable free.
9. Slide the power-switch cable out through the front of the computer.
Installing the Power-Switch Cable
1. Slide the power-switch cable in through the front of the computer.
2. Secure the power-switch cable to the chassis.
3. Thread the power-switch cable into the chassis clips.
4. Connect the power-switch cable to the system board.
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