Did the 40A fuse blow? If so you may have a short somewhere. A lot of reports of the wires to the fan motor heating up, melting the insulation, and shorting together. If the fuse was OK then check the 2 wires going to the plug next to the fan motor. Blue with a red tracer is the 12V from the 40A fuse. Blue with a black tracer is coming from the motor looking for ground. Should be 12V on both of them with the plug still in. That checks the wiring from the source through the motor. If you can jam a piece of wire into the plug with the blue/black wire, the other attached to ground, the fan should run on high. If so you have either a bad blower switch or a bad blower resistor. The resistor is attached to that 4 wire plug behind the motor, mounted in the plastic airway. 1 phillips screw takes it out and you can check it out. Probably the highest failure rate item in the circuit because it dissapates a lot of heat.