How to make a SCSI-3 terminator?
All the answers and information you need are on the Wikipedia page about Parallel SCSI

It mentions that SCSI-3 requires active termination instead of passive.

It then goes on to talk about termination:


  Active termination means that there is a small voltage regulator which provides a +3.3 V supply. Each signal line is then terminated by a \$110\Omega\$ resistor to the +3.3 V supply. Active termination provides a better impedance match than passive termination because most flat ribbon cables have a characteristic impedance of approximately \$110\Omega\$.