The back plane is a 4 pin connector, the connector from the PSU is 6 pin, the back plane only needs 12V (yellow and black) (documented in Intels PDF for that server chassis, see below, however can no longer be found on Intels servers!), the 2 extra pins are red (5v) and orange (3.3v) both needed for the SATA SSD drives.
So the above listed cable is a pass through cable, connects to the PSU power and passes to the back plane, if its not used the back plane will take the pin connector and only mate with 4 pins (from diagrams i have looked at).
Back plane power reference (document now cant be found but was on the below location)
This proves the chassis R1304SPOSHORR uas 4 x hotswap and 2 x cold swap drives:
Would this cable and plastic clips be part of the Intel FR1304E3V5ESK