I recently bought a hard drive off ebay with a macintosh plus and when ever I boot the macintosh, the screen stays black, but whenever I boot of floppy it works. The green drive light stays on too.
I think this is why it won't work. I've never seen ID8 on Mac SCSI devices. You can't set the switch to 8 on any of my Apple SCSI peripherals (Hard Disk 40SC, Tape Backup 40SC, CD300 and the CD SC). It only goes from 0 to 7.It also has a bip switch on the back, it is set on 8, but i think its the identifer
Echoing this. Maybe the head got stuck by gunk, and you can unstick it by doing what Bibilit said. And because the HDD won't work anyway, you can do it without being paranoid of breaking it.If the disk is not detected, you can have a try an remove the lid, then try to move the heads manually (don't touch the platter) you have nothing to lose.