Momentary dim with power window operation is normal, brake lights application may dim a touch. Car voltage is not perfectly regulated. My Dad's 2003 Toyota has a flicker effect in the dome light if the engine is on. I notoced it because it flickered more than my car. The battery charge level will affect load, regulation too, and alternator load is high after starting the car. It is nice to have another Contour handy to compare quirks .