If the connection is going from the mac to the scanner, the now empty port on your scanner will need a terminator on it.
The scanner might have a switch on the back to turn on/off termination so you can don't need to put on the terminator block. If it does, flip that and see if it helps. You might need to try putting the cable on the other port on the scanner too.
You can leave the ID at 2... or try 3, 4, 5... it's called SCSI voodoo for a reason
You can use Apple System Profiler (under the apple menu usually) to check out what devices are attached to your Mac.
Might also like to download a copy of good old
SCSI Probe and drop it in your control panels. All it will do it let you know if the computer is seeing your scannner (I suspect the apple app will accomplish the same thing though)