bolard

I own a 93 4runner 3.0 auto, While trying to start my Runner yesterday I heard a clicking sound coming from my main fuse panel under the hood, found that the 15amp EFI fuse had blown, installed a new one turned the key and pop! it blew, Could not find any obvious wiring issues , even checked to o2 wiring,all looks good , The fuse blows when the key is turned to the on pos, any advise would be appreciated, I Hate Electrical probems...