ARRRGH!!! Electrical problem in my Safari

Help please!! ANy suggestions would be great. I have a '93 Safari that is driving me nuts! About 6 weeks or so ago, I went to start it, everything died, and I smelled smoke. When I opened the hood, I saw a burned out fusible link, which I replaced. The next day, it burned again, and when we went to hook it up, the circuit was hot, even with the key out of the ignition(I know you're supposed to disconnect the battery!!). I decided there was something up, so I took it to the mechanic, they looked at it for 2 days, couldn't find the problem, but theycleaned up some corrosion on the back of the fuse block, and it ran fine until last week. Same problem, got it fixed, it happened again, and this time I asked them if they could replace the fusible link with an inline fuse, so I could replace it 'in the field'... They also replaced an ignition switch they hads replaced earlier, in case that was the issue. Still no dice, the thing will run for awhile just fine, then one day it will just take a dump. Every time but once, it has happened RIGHT as I start the engine, I turn the key, and everything dies with no crank from the starter.. Tonight, it did it while my fiance' was pulling out of the carport, but it could have been the moment she turned on the lightss. When I went to replace the new fuse, it immediately arced, and was useless, of course.

Any advice on WHERE to look for a problem, and what to look for? With two kids, and two working adults, we can't use just one car!! ANy help would be greatly appreciated.
Thank you!

Oops!! I forgot to mention that last week when the van died, the battery was actually spitting acid, and completely trashed, and when it happened two days ago, the NEW battery was smoking!! I obivously have something putting a continuous high drain on the circuit...

Sounds like a good time to get out the multimeter and check for a short to ground, it could possibly be the starter if thats the fusible link that blew, or if the crank wire is on that circuit. I'm not familiar with the Safari but this is where I'd start along with checking for wires with melted insulation