I agree with sparkytim, its usefulness is very limited as a testing tool. It would only indicate a voltage and what that voltage was, but nothing else really.
Break ring, energise one leg, and trace cable run - use voltage indicator to test at accessories. Not proper fault finding tool, but very useful at times.
Is it purely a voltage indicator or does it have continuity setting (ie Any batteries in it?) Mine has and can be slightly more helpful in certain circumstances.