IBM 7380E1U Installation And User Manual page 120

13. Make sure that the AC power LED on the top of each power supply is lit,
If you have other devices to install or remove, do so now. Otherwise, go to
"Completing the installation" on page 105.
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IBM System x3500 M3 Type 7380: Installation and User's Guide
indicating that the power supply is operating correctly. If the server is turned
on, make sure that the DC power LED on the top of the power supply is lit
also.