Dell OptiPlex 755 - Manual (Page 74)

DC Power Connector P2
DC Power Connector P3
DC Power Connector P4
DC Power Connector P5 and P6
21 +5 VDC Red
22 +5 VDC Red
23 +5 VDC Red
24 GND Black
*Use 22-AWG wire instead of 18-AWG wire.
Pin Number Signal Name 18-AWG Wire
1 GND Black
2 GND Black
3 +12 VDC Yellow
4 +12 VDC Yellow
Pin Number Signal name 18-AWG Wire
1 +12VDC Yellow
2 GND Black
3 GND Black
4 +5 VDC Red
Pin Number Signal Name 22-AWG Wire
1 +5 VDC Red
2 GND Black
3 GND Black
4 +12 VDC Yellow