Assuming the 2005 blower motor control circuit is the same as the 2006 SRT, you should check fuse B1 plus check/replace the blower motor relay. When the ignition key is turned to RUN, the blower motor relay is energized, and it appears to be energized no matter what position the fan speed switch is at, even the Off position. 12 volts goes through 40 amp fuse B1, then through the blower motor relay contact, then through the blower motor itself, then it goes to both the blower motor resistor block and the fan switch. When the fan switch is at the highest speed position, it connects the motor to the 0 volt return (negative terminal of battery). When fan switch is off, the blower motor has no connection to 0 volt return. When the fan switch is on but not at highest setting, the blower motor voltage path goes through the blower motor resistor block, then goes through the fan speed switch to 0 volt return.
Remember, this assumes the 2006 wiring diagram I am looking at works for 2005 as well.
Checking fuse B1 is easy. Replacing blower motor relay is easy and cheap. Beyond that, you should probably go to the dealer, especially if you don't do electrical work on cars.
