The last couple of days, my '88 740 non turbo sedan has been having its headlights, windshield wipers, radio, and other electrical devices getting slowly but progressively weaker. I first noticed that the headlights had gotten dim enough that I was having trouble seeing well on country roads at night, which is obviously not a good thing. The car otherwise seems to be running and starting okay so far, but I assume something bad is about to happen. What exactly causes the headlights to get dimmer with the car running? I suppose it has to be something wrong with the electrical/charging system. Is it the battery, alternator, voltage regulator, or something else? The accessory drive belt that runs the alternator is old and moderately badly worn. Would putting on a good new belt at the proper tension solve this problem, or would I be wasting my time? I'd like to figure out the problem soon so that I can correct it at a time and place of my choosing rather than getting stranded somewhere.