Toyota Repair: electrical-tail lights, brake light switch, corolla wagon

Question
Tail lights on '90 corolla wagon work ok when headlights are off. But, when headlights are on, the brakelights look "stuck" in the on position (bright), with no change in light intensity if brake pedal is depressed. Any ideas as to the cause?

Just prior to the occurrence of this problem, I had my rear-view window replaced (pumpkin was thrown through...but brake lights functioned ok with headlights on at that time), but the shop which performed the replacement claims that they're not responsible for my most recent woes.

Answer
I'm confused, is the problem with the brake lights or tailights, there could be a problem with the brake light switch or the combination switch on the steering column, or a wiring problem, it seems to me that if you did not have this problem before the repair of the rear window then it would sense that it had something to do with it.