this is a comment in one of the addons i use Called Mappy that handles minimap alpha
Code:
-- Force the alpha to 1 if we're indoors. The minimap doesn't work
-- properly if the alpha isn't 1 (it'll just show solid black) while
-- indoors (in this case, indoors means any major city, inside any building, any dungeon)
-- Detection of 'indoors' is imperfect however, so there are still times that the minimap
-- will go black when you don't want it to
go try it outside and see if it works