Most commonly this is caused by a defective ignition switch, and usually includes two burned terminals in the connector. Usually you will see the black terminals in the switch and the melted part of the plug when those parts are inspected. If you find that, it is critical that those two terminals in the connector be replaced along with replacing the switch. If either part of the repair is not done, the blackened parts will cause high resistance which translates into heat, and the new part will be damaged again.
This happens most often to owners who use the heater fan on the highest speeds often, and those who switch the ignition switch on and off when the heater fan is set to those higher speeds. The high current drawn by the fan motor heats up the ignition switch contacts, and there is excessive arcing in the ignition switch when it is turned on and off under load, meaning the fan motor is running on "high".
On most models, the radio is also on the same circuit as the heater fan and power windows, so if that does not work, it further points to the ignition switch. In rare instances two mating terminals in a connector under the steering column can become overheated and cause this same problem. This can start out as an intermittent problem but it will not be long before it becomes permanent.
Friday, April 6th, 2018 AT 5:33 PM