electrical malfunction
 

Hi, I need some advise, if anyone can help me. At night when I shut off the ignition, the next moring my battery is dead. Also, the interior lights when you open any door go on but extremely dim. The check engine light is on constantly and the air ride system does not activate. When you erase the check engine, the air ride system is activated. But, the battery still dies the next morning. Has anyone got an idea what I can check or what is the problem, or any part that can be replaced?

Under the passenger seat there are 2 computer boxes. And on the front driver side 1 computer box. If one of these 3 computer boxes is the problem, which one could it be?

It is a 1994 range rover, V8, 4.2L Any advice would be appreciated