The 80's I've had have been fairly reliable, well, except for one, which is currently in James1095's hands. Got one in my II, which came out of a IIci that I parted out. Works great. Loud, but no problems. Is one of trhe old half-height drives. They're not as bad as the Miniscribe 20's that seem to have come with most SE's. Those all seem to be dead.
In any case, look for a two pin connector at the opposite end of the circuit board from the connectors for power and the SCSI cable. If there isn't anything, then you'll just have to rely on the sound of the drive grinding away. Got a 250 in my IIci which has a built-in LED. Can be seen flashing through the floppy slot at certain angles.
Mac: 512Ke, Plus 4/0, SE 4/40, SE/30 8/40, IIx 8/230, IIcx, IIci 20/250, Q660av, iMac G3/333 Tang, G4/1.2GHz DA 1.5G/40G/DVD-RW, G4 MDD 2G/80G/30G/DVD-RW, C2D 2.16 iMac 2G/250G
Apple II: ][, ][+, //e x2, //c
Other: iPhone 4, Dell D830