[Chaplin]

That is usually the sign of a bad alternator. Assuming your charging system is operating properly, once the car is started, the battery is out of the picture and the juice to run the car is provided by the alternator. When the alternator quits and stops working, the car is then forced to draw its power from the battery, which it can do until the battery starts to die. When the alt. is no longer charging, and the battery has been drawn down, all the lights start to dim and eventually all electrical power is gone.

Oh wait a minute, you said dim-bright-dim, not dim-dim-dim. Start with the grounds and make sure all electrical connections are clean and tight, then check the alt. and battery.

Good luck