No, you don't need to open your Mac to add SCSI.
Termination:
A SCSI chain must be terminated at both ends. If your Mac has an internal HD, then that HD should be terminated (unless someone's been fiddling). Then, you just need termination at the last device, which in your case is the SCSI Zip drive. That's what the slider switch does. Switch it on.
However, if the Mac does not have an internal HD, then you need two terminators. This Mac is the Mac Plus. It needs a pass-through terminator connected right into its SCSI port. Then you could connect a SCSI Zip drive, and you'd still set the Zip drive's termination switch.
Other external SCSI devices, such as the Apple CD-ROM drives, don't have this termination switch feature. For these devices, you really do need a terminator block (generally Centronics).
What does termination do? Well, it's supposed to keep the electrical signals from "bouncing" back down the chain and confusing the other devices or your Mac. Some people can get away without using terminators, others don't.
Termination:
A SCSI chain must be terminated at both ends. If your Mac has an internal HD, then that HD should be terminated (unless someone's been fiddling). Then, you just need termination at the last device, which in your case is the SCSI Zip drive. That's what the slider switch does. Switch it on.
However, if the Mac does not have an internal HD, then you need two terminators. This Mac is the Mac Plus. It needs a pass-through terminator connected right into its SCSI port. Then you could connect a SCSI Zip drive, and you'd still set the Zip drive's termination switch.
Other external SCSI devices, such as the Apple CD-ROM drives, don't have this termination switch feature. For these devices, you really do need a terminator block (generally Centronics).
What does termination do? Well, it's supposed to keep the electrical signals from "bouncing" back down the chain and confusing the other devices or your Mac. Some people can get away without using terminators, others don't.