Correction: '99 Headlight problem

In my previous post I mestakenly entered '89 instead of '99. To repeat:
     There is a fault in the headlight circuit in my '99: The headlights
come on with the headlight switch in the center and right positions even with the ignition turned off. I have normally left the headlight switch in the right position, and leave it there after parking, but now the headlights stay on and drain the battery. When I turn the headlights on, the radio/clock display dims like the voltage is being drawn down. What would cause this? Any advice will be appreciated. Thank you.

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