Look at the field wires in the generator to insure they are isolated from the ground, IE not touching ground. Since it melted the bracket the short is pretty close to that area. Insure that the mounting bracket is grounded/not grounded properly, check wiring diagram. The path of curent seems to have went thru the brush holder and not the brush it self. Sometimes when this amount of heat occurs the wire solder is melted away from the brush. Replace the brushes. I get mine from a local company that sells tractor parts, same brush and a lot chepper that vendors. Good luck and keep us posted
