on the resivor bottle there is a little plunger that sits inside the bottle , it must not be pushed down , so i would unscrew the top as if you were going to fill up the brake fluid , on the inside of the cap , push the plunger out and refit cap , and that might get rid of your handbrake light , the little plunger must not be pushed down as your car will think it needs brake fluid which causes the hand brake light to come on