The problem is the fact that HDD motor have 4 pins rather than 3.
What is 'negated signal' ?
From the schematic : Which one is negated by which one ?
Unfortunately this doesn't get clear from the article. I would just try and attach a scope to two pins. The scope output will show you quickly which are the right ones. Probably this changes from one drive manufacturer to the other, so you have to check anyway.
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