Dell PowerEdge R415 Systems Guide De Mise En Route page 6

Optional – Connecting the Keyboard, Mouse, and Monitor
Connect the keyboard, mouse, and monitor (optional).
The connectors on the back of your system have icons indicating which cable
to plug into each connector. Be sure to tighten the screws (if any) on the
monitor's cable connector.
Connecting the Power Cable(s)
Connect the system's power cable(s) to the system and, if a monitor is used,
connect the monitor's power cable to the monitor.
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Getting Started With Your System