Jumpers are on each drive, they are not master/slave as on ATA drves, but there are tree (or more of them).
each jumper represents one bit for ID, ie.:
Open Open Closed means ID 1,
Open Closed Open means ID 2,
also drive on the end of cable must be terminated and hadddrive in dhe middle must NOT be terminated.
there is additional jumper (terminator on/off) for that on most drives.
its best to start with drive sumper settings, you can found it on anufacturess site as PDF manuals.
hope it helps a little
edit: quick scsi guide
http://homepages.ihug.co.nz/~miles.j/amiga.html#CPUSCSI
