Not sure about this model, but with SCSI generally you want motherboard->internal-drives->terminator, then the last device at the end of the external chain gets a terminator. You need to make sure there's no conflicts in IDs as well. You'll want something like SCSI probe to help you debug.

With some weirdo setups, it helps to have a device in the middle have a terminator. Not sure if this was an old wives tale or real, but it can't hurt to try.

Beware that some SCSI devices are differential, so be sure you know what kind you have, as you can't mix differentials with regulars. I think off the top of my head that the IIfx used differentials, so needed special terminators and all differential SCSI devices.

http://www.openbsd.org/38.html OpenBSD has a song about SCSIs. Sort of.