Test the electrical circuit's ! Look at a wiring diagram so you know what wire's to test . Watch these video's , buy a DVOM - digital volt ohm meter . Learn to test so you don't listen to guesses .
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Free wiring diagrams here . http://www.bbbind.com/free_tsb.html
Enter vehicle info. year , make , model and engine size. Under system click on lighting ,then under subsystem click headlamps . Click the search button then the blue link's . Right away in the first diagram i see the headlamp / panel dimmer switch is a input to the BCM - body control module . I mite think your first response would be to want to replace the BCM ! Reading a discription of how the lights are suppose to work may shed some light on the problem .
Headlamp ON/OFF control is determined by the body control module (BCM) by a signal on the headlamp switch on input circuit when the headlamp switch is in the HEAD position. When the headlamp switch is in the AUTO position, the BCM determines headlamps ON/OFF by the voltage from the ambient light sensor.
If the headlight switch is left in the ON position, the inadvertent power control feature will turn off the headlights approximately 10 minutes after the ignition switch is turned to the OFF position. If the driver places the headlight switch in the ON position after the ignition switch has been turned OFF, or if the ignition switch is in the ACCY position, the headlights will remain on until turned off or the battery runs dead.
The high beam indicator is illuminated when the instrument cluster receives a class 2 serial data message from the BCM that the high beams are illuminated.
Having the vehicle checked for DTC'S - diagnostic trouble codes , BCM - codes ! Need a professional type scan tool . Part stores can't read body codes , dealer or independent repair shop .
When the body control module (BCM) senses a request for low beam headlamp illumination, the BCM sends a ground signal to the low beam headlamp relay through the headlamp low beam relay control circuit. The headlamp low beam relay will apply voltage to illuminate the headlamps.
When the body control module (BCM) receives a ground signal from the multifunction high beam or flash to pass (FTP) switch commanding to illuminate the high beam headlamps, the BCM will energize the high beam relay by grounding the high beam relay control circuit.
The body control module (BCM) receives a variable voltage signal from the instrument panel (I/P) dimmer switch requesting to illuminate the illumination lamps to a desired intensity. When this occurs, the BCM directly sends a variable voltage based on the I/P dimmer switch position on the instrument panel lamps dimming supply voltage circuit, instrument panel lamps dimming control circuit, and the LED dimming signal circuit.
Voltage for the instrument panel lamps dimming supply voltage circuit, instrument panel lamps dimming control circuit, and the LED dimming signal circuits is from the TBC 2 A fuse in the instrument panel fuse block directly through the BCM to these circuits.
The BCM directly sends a 5 volt reference voltage to the I/P dimmer switch which is then adjusted based on the I/P dimmer switch position and returned as a dimming return and dimming input to the BCM. The BCM uses this signal to directly control the desired level of instrument panel illumination lamp intensity.
Your best bet , take it to a qualified repair shop .