SCSI bus should be terminated on both ends and nowhere else.

Either to plug termination block to both ends of cable or switch ON
termination block integrated to SCSI devices connected to bus ends (and
switch OFF all these blocks on devices in the middle of bus). Note that
"bus" is not equal to "cable"! One end of cable is usually attached to SCSI
controller device and for proper termination you should to check controller
device manual. Usually this end of bus is terminated by default. But if you
have "single chip" controller with two connectors (internal and external for
example) and you want to use both, it is possible you need to turn  its
internal termination block off. If you are connecting new device to
functional bus, plug it to the middle of cable and be sure its internal
termination block is not set. If you are making new bus, plug controller to
one end of cable and other device to the second end of cable and turn on
both termination blocks. If device has not internal termination block,
either use passthru termination block to connect it to the end of cable or
terminate end of cable by cable termination block and plug unterminated
device to any of middle connectors.