a While ago while winching I had a ground wire in the drivers rear corner go up in smoke. Not sure why as the winch is grounded directly to the battery. It was a puny little ground wire that combined many other ground wires. So I replaced it with a larger size.

On the weekend I had the same thing happen! I haven't looked at where it melted but it happened while winching again and now my left rear brake/turn doesn't work and my gas gauge is wacked.

any ideas as to what would cause this?

You have a bad ground going to your battery still, make your own cables with brass ends and solder them, if you buy the store bought junk that has a steel end smashed onto a copper wire that is just lame, throw them away as far as you can, the only way those will work is if the stud touches some of the copper wire inside the hole of the cable end, I would hate to see the odds on that! that goes for starting cables also, get like a napa gold wire if you are to lazy to make one.

i still use the stock wires in my car and i run a little over 3.7k watts that should be as much draw as a winch. just clean up all the grounds and if they look rotted at the end chances are they are rotted down the line to.

is there alot of gunge ontop of your batter around the cables?