Back in the day, working with WD was a nightmare. The spinning HDs never came with a keyed IDE cable. It must have saved them $.0001 per HD shipped. If you accidentally put the cable in backwards, it not only burned out the logic board on the WD HD, it would also burn out any other drives on the cable. And the IDE controller on the motherboard.
Now it is easy to remember how to do it right. Install the power cable and then make sure the red wire on the power cable was next to the red wire (pin 1) on the IDE cable. But if you rush or make an assumption, that was an expensive mistake.
This sounds like maybe early 90's possibly without voltage regulators at the molex connector. I've been doing this a very long time and have never heard of this.
I've serviced computers where the ide cable key was hand-striped or with some other marking with a marker as opposed to the line (spoon's red wire) already keyed from factory, somewhere mid 90's. regular procedure at that shop i think at that time to mark any unkeyed cable found. not that i ever had to mark any single one, so even then they were really old ide cables.
Actually...i kind or remember a motherboard coming up in smoke from one of those when someone made a mistake. brand new first week technician i think.