BMW Repair: electrical system short, 1992 325i bmw, mechanical side

Question
1992 325i bmw - I need help, I love my bmw and I think it's fried...my battery rusted through the trunk and made contact with the frame of my vehicle, causing a complete system shut down while driving 70mph on the freeway. Where do I start in trying to analyze the damage?
thanks in advance for any info you can give!
Jessica

Answer
Jessica,

 It sounds bad, but I dont think it's TOO big of an issue.  Hopefully all that happened was the battery is shot.  You need to replace the floor in the trunk so the battery will have a place to sit.

 Any competent body shop that fixes dents and wrecks should be able to weld in a piece of metal for you.  You can call the dealership and see if the trunk floor pan is available, but I think the bodyshop could bend a piece and have it work fine.  They should coat it again to prevent any future rust from forming.

 On the mechanical side, I would get a new battery and try it out.  Hopefully all that went bad was the battery its self.  A battery has two poles (+ and - ) and if they are connected they will spark.  Your whole car is connected to the " - " or the Ground.  As soon as the "+" pole touches ANYTHING metal on the car, it will complete the circuit and "short out".  I'm hoping that your computer didn't get hit by the voltage irregularities.  

 So right now, I would get the floor pan fixed, shouldn't be too much to weld in a new piece of metal.  then replace the battery and the car should start.

 Hope this helps,
 Josh