IBM RT User's Setup Manual page 194

8. Look at the diagram of the power cable. The 4-pin connectors
connect as follows:
• P10 is connected to the power supply.
• P ll is connected to the first diskette drive, position A.
• P12 connects to the second diskette drive, position B.
• P13 connects to the first fixed-disk drive, position C.
• P14 connects to the second fixed-disk drive, position D.
• P15 connects to the third fixed-disk drive, position E.
Section 2. Removing and Installing Drives in IBM 6150 2-19