It seems to have used the flat ribbon's ground pins for ground return... :crazy: Electricity finds its own way. Those ground pins are signal ground and not power ground.
This is not at all recommended: the flat ribbon and the IDE plugs are in no way supposed to cope with the current flowing through them that way - some drives need >>1 A on startup (esp 7200 RPM ones).
Use a seriously dimensioned cable to add a ground line and if possible get a new IDE cable, yours might have been damaged by that abuse.
