Blown Fuses

The other night my daughter's 1999 KIA Sportage died at an intersection. She tried to start it, but it would not turn over. I checked the fuses in the engine fuse box and found that the main fuse (15A) was blown. I replaced the fuse and the vehicle started up fine. Yesterday, the same thing occured and again the main 15A fuse was blown. What could be causing this and where should I look for the problem.

Just in case, this diagram
www.geocities.com/lmp4203/kiasport/PowerDist.jpg
although it does not tell a lot...
some more details on page 25... www.geocities.com/lmp4203/kiasport/Injection.PDF
it seems it feeds only the computer and a few sensors.
So I'd rather think for some pinched wire.....may be disconnect canister purge solenoid for a test..... www.geocities.com/lmp4203/kiasport/kiapurge.jpg