I contacted Husqvarna and their rep stated that the "O" is the on position, not the "---" although they had to ask someone. It's pretty stupid that they did not use the words on and off. Either way, I believe I tested it in both positions just in case but maybe I did not let it run long enough, I Was told that you should feel the grips get warm in just a matter of minutes, if that.
Are you speaking from experience Eugene?