Sounds like ya got a dead short there, one way to see is to remove the pos battery cable, now get out your trusty 12volt test light, hook one end to the POS cable and the other end to the POS post, if it lights up you got a short, if so you got to start hunting, now to narrow your search down a little leave the light hooked up and lite, pull fuses out one at a time and when the light goes out you'll have narrowed down the seach to what ever is protected by that fuse, if no fuse makes it go out, all thats left is main wire to starter, starter itself (very rare) or some kind of add on device hooked right to the battery itself, hope this helps some.