well it could be caused from a few things, but i did notice it looks like they re attatched the black and oranges which i think we have came to the conclusion that is a NO NO!
you want a 4ga power wire going from the back of the alt lug, to a 150 plus amp fuse holder, and from there it goes to the positive post on your starter selenoid.
disconnect those black and oranges from the alt and cap them off individually and let them hang or tie them back, then replace your 4 g if it's melted with new 4g and an in line fuse.
always check all the other wires in that harness to see if any of them have been melted and replace accordingly.
that harness has someother wires of need. one of them is a green wire that goes to your bat light, the other one is a yellow wire that joins to the black and oranges, that turn into another green wire that connects to the starter selenoid positive side.
you may have to remove that harness to check to see how bad it is.. you should probably just buy the 3g conversion plug, keep the green wire in the harness that goes to the battery light and scrap the rest.....but for now, check to see what other wires are melted if any and disconnect those black and oranges and get a fuse on there....
also, here's a wiring diagram, courtesy of tmoss, it shows how the stock wires go so the above makes better sense. sorry for the size of the diagram, it gets distorted if i reduce it too much so i left it alone.....