Mine was the fan speed switch, that started to melt. The blower motor starts to wear and pulls more current. The wires to the switch cannot handle the currrent so the switch melts. You can replace the blower motor, and switch, and this will stop it until the motor starts to wear again. I did the relay mod, and replaced the blower motor, and the whole dash unit. Now it will not melt the switch. Do a search on Relay mod, or melted fan speed switch.