the connector on the heat duct is the "heater resistor", the switch runs the current for the motor through this to drop the motor voltage to provide low and med fan speeds, hi speed is full voltage directly to the motor. if low and med speed work ok the resistor and it's wiring must be ok. Be sure it has the right rating of fuse, hi speed will be maximum current, if the fuse is rated too low it could blow it. if thats ok, try to take a jumper wire from the heater wiring(before the switch) directly to the motor and see if it blows the fuse, if it does the motor must be the problem, if it doesn't the switch or hi-speed wire must be shorting out,then use a jumper on the heater switch from the supply terminal to the high speed terminal, if it still shorts out it must be the wire, if it doesn't it's probably the switch. hope this helps.
