Legend won't start-battery dies

We have an 88 legend coupe. what happenned is that the car won't even turn over. When/if the battery is left hooked it drains. Took it to a mechanic and he said it was a fuse and then the car would start. couple days later the car did it again. won't bump start either. No Spark. Looked in the fuse box in the engine bay and the ignition and all the fuses looked good. Is there a fuse box elsewhere in the car? Why does the battery discharge? What to do?