In these machines +/-12V is only used for Audio op-amps, RS232 Line drivers and the floppy motor. everything else is running on the 5V rail.
Too low current on the -12V rail can cause crackling sound. I use my A1200 machines mostly for this, although more using AHI than before.
External drives should have their own power supply and indeed the A590, A570, GVP drives etc all do.
The A500/A2000 Technical Reference (page 227) shows that the 12V current limit on the expansion connector is 50mA
The A600/1200 don't even have the expansion connector
Page 5 of the TRM specs the -12V supply at 100mA
> Too low current on the -12V rail can cause crackling sound.
Maybe if the current is zero
TRM: https://archive.org/details/CommodoreAmigaA500A2000Technical...