Having Electrical Problem Blowing Brake Light Fuse

[Desert Rat]

Electrical is not my area of expertise.Just recently my truck started popping the tail/brakelight fuse. and recently when i start to put the key in the ignition it sparks.anyhow upon putting a new fuse in it sparks and pops as soon as i put it in(yes with key and headlights off)did this with 4 fuses(correct amps)unhooked battery put one in,as soon as i hooked battery back up it blew again,so this morning in the dark,i used a bypass jumper wire(not something i care to do)and on the way to work about 2 miles it melted the thick gauge wire.any ideas,of where to look? i know everyone will say check your grounds,been there unless i over looked something?it was fine when i last parked it,but blew on its own while sitting,and theres power there when key and lights are off.Any help very much appreciated.