Battery drain

I have checked every thing. I had negative cable disconnted with test light connected clipped to disconnected negative cable and the probe connected to the negative post on battery with brite light indicating some thing shorting out. Then I disconnected the battery cable that goes to the fuse module box under the hood and the test light went out. I connected the cable and pulled the battery 50amp fuse and the light went out. I think all that fuse supplies power to is the radio and the illumation lights that I know of. I dont know where Im able to disconnect either of the item to ellimanate either item. What are your reommened steps to fix problem