Want to install aSeagate Barracuda 9 Gb. wide SCSI drive in an older PowerPC which has been upgraded with a Sonnet G3 upgrade chip.
The hard drive model is ST39173LW which has cables for its wide SCSI and an Adaptec controller card;(AHA-2940W/2940UW)
I've tried installing it;
reset the little button on the mother board;
I can't get the Mac to see it;
It has jumpers, of course and I haven't been able to understand the diagrams which tell how to assign it a different ID#;

Usually SCSI device letter wont matter unless they're conflicting, but this is a MAcintosh, *sigh*

Not all scsi drives will work in the older Mac's. The older
drives are just not as compatible. Was this drive ever used
with a Mac? Is that adaptec card the Mac version, because
the PC version will definately not work. With that said, go
the seagate web site and search for the diagram of your
particular drive, they will usually have a jumper pin layout.
Make sure the drive is terminated properly too. I have not
tried your particular drive before, but in my past
experience I have been able to get most seagate drives
that are wide (ends in W) and ultrawide (ends in UW) to
work. Never had a drive that is designated LW. Good Luck.

The drive specs are at http://www.seagate.com/support/disc/scsi/st39173lw.html

Normally the internal hard disk is assigned SCSI ID zero so I would assign the second drive ID one. Make sure the other jumpers are in the positions called for in the diagram as being their factory defaults. There is one exception: set the jumper to "force single-ended operation".

I just went through dropping a 9GB IBM disk into a Mac II. I had the same symptoms until I had the jumpers the way I described above.

Also, as the other person points out, once the Mac can see the drive at the hardware level, the first thing it will want to do at startup is load a driver from it. If there isn't one, the drive won't mount and thus won't be visible on the desktop. This is normal with blank drives and with those coming from other computers like PCs. Go get FWB Toolkit (www.fwb.com), a highly rated program. This app will see the disk just sitting there and will let you format it, or if the format is already OK, to just replace ("update") the driver.