Very Wierd Electrical Issue
 

I have an issue that is puzzling me. I parked my blazer for 2 days and after heavy rain, no flooding, from hurricane sandy here in mass it wouldnt crank/start. I got it turned the key on everything lit up, turned to start and boom everything OUT, then after that I turn the key and get dim and minimal lights in the dash, dinger stays steady and sounds wierd. I hooked up jumper cables, it cranked hard but started. ran great, shut off and started hard again with jumpers, but with just the battery it wont do anything. I drove it home and while driving home it ran and drove great but all the suddon the all the lights came on just like i had turned the key on. went through normal startup process and all gauges went back to normal. got it home, still wouldnt start on its own, locks act like very low power, tried with a differant battery and same problem. rear hatch popped itself open at one point. anyone know what it could be? I dont want to keep changing parts until I find it, hopefully someone has an idea!

Sounds like you have a ground short because of moisture.
Something is grounding out & causing electrical demons!
Might be a ground wire, check the fuse box under hood for wet connections as well, the connections to the alternator & starter. Are the battery terminals clean & solid?

The connections are clean. I am going to get it to my shop and go through it, this should be fun.

I would suspect the ignition switch... They are known for giving weird electrical issues like this. Just a thought. Let us know what they find.