The red wire on the ribbon cable should be facing towards the power connector on the HDD. You will also need to terminate the end of the chain, which for you is the HDD. The SCSI HDD will have some sort of jumper selection. Study the Jumpers carefully and set the drive to your chosen SCSI ID and also look carefully for a jumper for termination. Look up the Model Number of the drive in google, you'll probably find a document with the jumper settings outlined clearly.
If you cannot find a terminator on the drive, then you will have to place the drive on any 50pin connector but the last, you will need to apply a passive terminator for a 50 pin ribbon cable to the last plug at the end of the ribbon cable
