Headlights problems of the 2001 Buick Lesabre

While driving at night 2001 Buick Lesabre lights malfunction. (11/16/05) the lights would go dim.

At night, raining, on interstate 95 near freeport, me driver fiddling with wiper speed control (he thinks), headlights go out for 2 to 4 seconds (it seemed like an eternity) and then come back on. Was able to repeat while parked, later that night, also raining. Hawe not tried to repeat. Took car to local Buick dealer (not the one purchased from). Mechanic unable to repeat, even by blocking light sensor on dash and squirting water on rain sensor on windshield. Mechanic says he called somewhere in gm and was told that in maine, it is required that headlights come on with wipers. Referring to driver's handbook, noted that setting the "twilight" control to off might cause problem but driver does not recall fiddling with that knob. It is possible that twilight knob had been previously set to zero. This car has every possible option, wanted or not and is presumed to be idiot-proof. It is however a very scary situation and I want it fixed please.

Unable to turn off headlights using light switch until ignition switch is switched off. Had contacted dealership. Please provide further information.