IBM RT User's Setup Manual page 237

2-62 Options Installation
8. Connect B on the cable to the 34-pin connector on the rear of
the second diskette drive.
9. Connect P12 on the power connector to the 4-pin connector on
the rear of the diskette drive. (See page 2-29 for a diagram of
the power cable and connectors.) Connect the ground wire to
the ground tab on the second diskette drive.