Asus P5N-D - Manual (Page 156)

6-4 Chapter 6: NVIDIA ® SLI™ technology support
7. Connect a VGA cable or a DVI-I cable to the graphics card/s.
We recommend to install an additional chassis fan for better thermal
environment.
5. Align and insert the SLI connector to the goldfingers on each graphics card.
Make sure that the connector is firmly in place.
6. When installing two VGA cards using a 20-pin ATX PSU with sufficient+12v
capability, we recommend that you connect the auxillary power source from
the power supply to the graphics card. Refer to the PSU documentation for
dual VGA power requirements.
SLI connector