This is an adapter which allows you to connect a Seagate drive to the COM port, allowing to access TMOS using any terminal program.
Connect GND to the ground (any wire in PC colored in black)
You can locate Tx and Rx by doing some experiments with jumper-pins of a drive.
WD_Caviar_24300_PCB_L2
WD_Caviar_24300_PCB_L1
WD4000YR-01PLB0_PCB
WD2500YS-01SHB1_PCB
WD1600AAJS-00PSA0_PCB
WD1500AHFD-00RAR1_PCB
WD400BB-00DKA0
IC35L060AVV207
HTS726060M9AT00
MHT2040AT
motor controller
Seagate RS-232 adapter schematic