I have just repaired my non-working T3 by replacing one of the IDE cables and the two cables that run to the front of the PC unit.
I was a bit concerned because the original IDE ribbon seemed to have a crossover on one of the threads which I couldn't replicate but the new cable seems to work fine with the optical drive.
I bought the cables from www.digikey.com - 0.5mm pitch, 5 inch (125mm) length and 50 pin for the IDE. They shipped to the UK from the USA in 5 days - excellent service.
I cannot guarantee it will work with your HDD but its worth a try.
Not so sure if they sell the actual harness as well - why do you need to replace these?
If you need the part codes I used, let me know.