1986 Toyota Camry Wont keep battery charged

First brand new alt was the first thing I did but that wasnt it. Problem started when someone tried to put a different radio in the car, the new radio never worked and I discovered an electrical nightmare of disconnected and exposed wiring hiding behind the face plate. The car will run for about 3 or 4 days then faithfully the brake light will start to come on whem I depress the foot brake or use the turn signal. The car will start to idle roughly and eventually will fade until it won't start unless I jumpstart it or recharge the battery on a separate charger. Any ideas what this could be?