I am trying to help out my Mother in Law. She has a 93 sentra. She had a dead battery so I replaced it for her. Before I did that the Brake and Alt light were lit. After replacing the battery everything seemed fine, nice charge, lights went out. Then when I went to put on the AC I heard the compressor kick in then a relay started clicking under the dash. When the relay was going on and off, the brake/alt lights were going on and off. If I shut off the AC the problem went away. If I left on for a minute or so the Brake/Alt lights stayed on again. This seemed to create a direct short. I removeed the battery from the circuit and the relay seemed to release and go back to normal operations. Question is, has anyone had this problem? Can anyone describe what relay might be cycling on and off? Any help would be appreciated.