Strange electrical problem 2001 626 4 cyl

[Hoosier56]

New to this forum with a strange question. My son's 2001 626 has a problem. The "open door" light on the dash is on 100% of the time and drains the battery overnight to the point the car won't start. If he pulls the cabin fuse, the light goes out and the car starts fine. We've been told he needs to replace the car computer, but on a substitue teacher's salary, that option is less than desirable. Any ideas on what could cause this problem would be appreciated. we've also been told to remove each of the door switches until the light goes out. We did that, but that hasn't helped. Thanks for any help.