Are there any pads for an LED or connector on the drive PCB? You might poke around with a logic probe and see if any of the I/O pins on the interface chip change states when the drive is accessed. Most hard drives I've seen do have some sort of provision for an activity light.

There were TONS of those 80MB Quantum drives out there, most late 90s 68k Macs I remember had them. I've had a couple of them fail myself too, although all these drives are old enough that it wouldn't surprise me to see them failing.