92 Mercury Sable Battery Keeps Going Dead

[coptercop]

The battery keeps going dead after sitting for 1-2 days. Just replaced battery. While at the auto parts store, the alternator was checked, it tested OK on their test equipment. I don't have a diagram for the fuse box. Which fuse is for the cigarette lighter? The car's stereo is also in bad shape. Sometimes it works, sometimes it doesn't. (Sometimes doesn't get electrical power). Any help is greatly appreciated. IF you can suggest any other places to check, just chime in. I'm all about trying your suggestions. Thanks.