99 drl problem

Something has failed in my '99 DRL circuitry. I have replaced the DRL module, but the problem is still there: When I turn OFF the ignition with the light switch ON, the headlights stay on. I used to be able to leave the headlight switch ON all the time, and it would turn on the running lights during daytime and automatically turn on the headlights when it was dark. When I open the door with no key in the ignition, the little light in the A/C vent flashes. I think this is normal.

Can someone please tell me what has failed? If not, can you tell me where to go to find the answer?

Thanks,

TP in Texas