A while a go I picked up a GSP (Guardian Service Processor) PCI card for my HP-UX systems. If you don't know much about HP's PA-RISC systems, A GSP is a Lan console so you can connect to the Serial console via HTTP.
You'd expect that a PCI card would draw all voltage from the PCI bus... yeah ok wake me up when that happens.. HP in there smartness have used a little cable, good luck on finding out what or where it goes.
Its a power cable.. 5v exactly. I recently got hold of a HP J6750 (More on this later) and I wanted to make a mod to power it that was nice and clean. So I found the 5v and GND termination points on the SCSI backplane. Its nice and close to the PCI cage to! So I just soldered two wires.. easy as.
See images below of final product :
The Black plug goes to the GSP card The two white plugs go into each other. You can see the two solder points on the backplane.
You can see all the pics of each part of the cable and backplane on my flicker