Are you sure your SCSI drive has a system that will boot a Plus? The symptoms sound like a software crash. There may also be some oddities about booting a Plus with a 68030 chip. What happens if you boot from floppy with HD attached? Termination / term. power OK for a Plus? Remember the Mac+ doesn't supply term. power - the drive for a plus is finnickier than for other Macs. There's also the matter that a Plus uses software timing to read the SCSI interface, and a 25 MHz 68030 is going to be moving bits a lot faster than an 8 MHz 68000. It may be reading bits faster than the drive is spitting them out. You may need a special SCSI driver for that machine.