2002 Vauxhall Corsa My battery stays on when ignition is of

I brought a new car stereo for my corsa at halfords and they installed it. Ever since my car battery continually drains after about 48 hours when not in use, so i return to a dead battery. If i disconecct the stereo will this solve the problem. Ive been told they have wired it to the wrong part and not the ignition wire.