I'm going to have to assume you did not follow Desmo's link, so I took the liberty of copying it and psting it here for you. If this is what your problem sounds like, or even just to be sure, I would suggest you at least take a look.
"Hey guys. Just letting you guys know to be carefull because I just caught something really bad in my 325is. I was driving one day and then all of a sudden things started to go really wrong. I lost my headlights, I had no interior lights, no dash lights, and no turn signals. MY OBC was going crazy saying all these electircal failures were going on. It was night and all that worked were my foglights to light up the road. I stopped by the dealership I work at and opened up the fuse box and saw about 10 fuses blown. I replaced them all and then they instantly blew out. Then we noticed something interesting, all my lights didn't work, except my tailights. They were still lit up. The mechanics traced all these problems to the wiring harness that goes from the car to the trunk. If you look on the left side, when your trunk lid is up, you see a thing of wires wrapped up in a black covering. We took off the covering and you won't beleive what we found.
ALL THE WIRES OVER TIME RUBBED AGAINST EACHOTHER AND THE WIRE COATING RUBBED OFF EVENTUALLY AND ALL THE WIRES WERE TOUCHING EACHOTHER. FROM YEARS OF OPENNING AND CLOSING THE TRUNK, THE WIRES GET WEAK AND SO DOES THE WIRE COATING. Mine was really bad, it went all the way into the car, luckily it stopped before it went deep into the car where I would most definetely not be able to reach it.
I RECOMMEND EVERYBODY CHECKING THIS OUT ASAP. SAVE YOURSELF ALOT OF MONEY AND PREPARE AHEAD. I INDIVIDUALLY WRAPPED EACH WIRE IN ELECTIRCAL TAPE.
IF THIS HAS HAPPENED TO YOU, POST. I can't be the only one.
UPDATE : YOU HAVE TO TAKE OFF THE BLACK PLASTIC COVERING AND THE RUBBER LIKE TUBE TO EXPOSE ALL THE WIRES BEHIND TO BE SURE IF THE WIRES ARE FRAYING. YOU WON'T BE ABLE TO TELL ANYTHING WITHOUT CUTTING THROUGH AND SEEING.
It makes sense that when you open and close your trunk that those wires are going to rub against eachother everytime you open and close."
<span style='color:green'>Nobody likes you.</span><img src='http://www.bmw-forums.com/forum/html/emoticons/ph34r.gif' border='0' alt='user posted image' />
<span style='color:green'>Are you experienced, little girl? I want to know what goes on in your little girl world.</span>
<span style='color:green'>I'm the man! I'm bad, I'm so bad I should be in detention. I'm the man!!!</span>