Lenovo 5458 Installation And Service Manual page 282

Figure 182. Power connectors
Figure 183. Correct way of connecting the power cable connector to the system board
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System x3250 M5 Type 5458: Installation and Service Guide
Attention: When connecting the power cable connector to the system board,
do not grab the wires. Grab the middle connector to vertically connect the
power cable connector to the system board.