Just came back from a 1500 mile trip loaded up with a camper and towing a utility trailer with out a problem. I went out to start the truck this morning and it made it 50yrds down the street and died. I noticed the autoshut down fuse (20amp) in the box under the hood was blown. Put a new one in and it poped as soon as I turned the key on. Does any one know what tiggers the auto shut down relay to cause this fuse to blow? I assume it is a circut designed to protect many things but I have no engine schematic to trace it out.