Grant,
That was my thought, too. For all the computers and all the power supplies over the years, I have never memorized the power leads for mac soft power. Do you happen to have a quick link to the pin out for various mac power supplies?
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brg 2630,
Here is a little more detail on what Grant is saying. If you take a power supply out of a PC and notice that it does not have an on/off switch, you have to ask yourself how the power supply turns on in the first place. The green wire gets a low voltage signal from the keyboard. That signal closes a relay that starts the power supply in full. If you want to use that power supply for a science project, you can take a paper clip, bend it into a 'U' shape and poke it into the green wire pin contact and the black wire contact beside it. That is how you hot-wire a PC power supply that does not have an on/off switch - in fact, even if the supply has an on switch, you may still have to trigger the supply using the green lead. Some energy save capable supplies may even need to see a load to stay on. More on that at in the wikihow site video.
In twenty five years and hundreds of mac computers later, I do not recall ever mapping the Mac power supplies. I just swap out with another supply. So, I can not say that it is the green lead that signals a mac supply. Something new to do.
Here is a wikihow page that discusses the idea in greater detail. Notice under "tips" that they give the option for skipping a switch by connecting the green and black leads.
http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply
So, for your computer, you first need to confirm that the power supply is dead. Meanwhile, the hard drive will hopefully migrate to a more capable machine.
Jim
PS Somewhere in the last ten years is a discussion post on converting an ATX style PC power supply to work in a Mac G4 or earlier machine. That will have the pin assignments listed. Unfortunately, the machine with that book mark is a hundred miles away right now.