My battery light is on and the lights are dimming.
These sound like the symptoms of an alternator failure. The alternator can cause all sorts of weird electrical symptoms if it has gone bad. While the battery is responsible for starting the vehicle, the alternator's job is to charge the battery while the engine is running so that the battery will have enough charge to start the engine again. If the alternator has gone bad, the vehicle's electronics will then start to run off of the battery alone. Once the battery's charge starts to decrease, the red battery light will illuminate and your headlights may dim. You may also notice that other electronics in the vehicle will quit working all together. I would recommend having your starting system inspected by a mechanic to verify that the alternator is bad, and have it replaced if so.
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