Found the problem. The red wire was frayed by the drive cage.
With another cable (nowhere near as long as the original) it worked fine.

Grrrr....

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haha thats what i thought, you should replace it with a third party made cable instaid of the one that comes with the imac to prevent a repeat of the problem.

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This is not an iMac, but a Blue and White G3 tower running at 400mhz. I needed to backup the data before I reinstalled Tiger, so I removed the DVD drive and connected a 30GB hard disk to the cable. Apparently it partially lifted up the data cable so when I slid the cage back in it caught on the cable.

The one used on the optical drive on this one is considerably longer than normal IDE cables and snakes around the inside of the case, under the hard drive try and finally connects to the motherboard. It's going to be a PITA to replace.