IBM RT PC Options Installation page 82

2-38 Options Installation
5. Look at the diagram of the power cable. The drive in position E
connects to connector P15.
6. Connect P15 on the power cable to the 4-pin connector on the
rear of the fixed-disk drive. Connect the ground wire to the
ground tab on the drive.
Note: Internal fixed-disk drives may differ in appearance.
Data, signal, and power connectors, however, remain in the same
relative positions.