Needing a solution to this problem (to get some feedback from my Vampire-2 MicroSD access) I stumbled upon this thread and this solution worked best for me:
http://aminet.net/package/util/moni/IdleLed
I tried to recompile the Modula-2 source to change led from power to floppy (which is unused in my system) with no luck, but alone works ok with POWER led.