If you have any add-on electronics, disable them until you get this figured out. The entire length of wire getting hot or just the pins in the harness? The wire harness for the blower motor in a prior car melted like that, but at a much slower pace. The cause in that case wasn't the blower motor or the resistor assembly. The contacts in the wire harness had corroded, which effectively turned them into resistors; converting much of the energy flowing through them into heat. I assume you bypassed the harness completely? If the wires are hot check the regulator's ground connection back to the battery. The alternator in a prior car ran the stator inside of it, full field until it burned out. Just replacing the regulator in that alternator made no difference so it was the stator that burnt out. Cause in that case was a weak connection back to the battery negative; confirmed via voltage drop test from alternator case to battery negative post. Stator in that alternator was ssuuppeerr hot and the regulator read over 15v prior to burnout. When wires are overheated, they tend to damage their insulation. So both the wires, wire harness and stator may require replacement at minimum. Partial operation may be a result of one or more of the regulator circuits faulting. Have the battery tested.