1. You may have a bad ground. 2. The battery may not be charging, due to a bad battery or alternator
The dim lights are probably caused by hazed,cloudy, or fogged out plastic lenses. I detail headlights at used car dealerships and I use a product called CrystaLenz. Their product works extremely well without removing the lens or using any special tools. You can get more info. at www.crystalenz.com
How does that even answer the question?
Your insturment pannel is currently set to auto dim. page78 in owners guide
Usually dim headlights are caused by a poor ground connection.
You've got a bad headlight switch and need to replace it, that's the switch you pull in the dash to turn the lights on. That's why the headlights only work on bright but not dim.
If the headlights are halogen, these tend to be sensitive to voltage spikes. Before replacing the headlights, have the electrical system checked for faulty voltage regulation.
the courteous time to dim your headlights is as soon as you see another vehicle, or within one half mile.
when there are oncoming cars, it is appropriate to dim your headlights when they are about 300ft away. Check your diver manual for the most correct answer.
Your headlights may not dim because you don't have dimmer lights. Dimmer lights can blow and leave you with just the high beams.
You should dim your headlights within 500 feet of the car in front of you. The rule of thumb is, if you can see another car, dim your lights.
If you can see the area lit by their headlights, then you are probably close enough to dim your own.
On my zx2 there is a button on the lower part of the dash by the drivers door that you can brighten or dim the lights... Not sure this is your problem but it is worth a try ... I use it to dim them when driving at night..
If by "dim headlights" you mean low-beams... the bulbs are bad and must be replaced.
The headlights on the 2002 Toyota Tacoma might work on dim but not on high beam because of a blown fuse. If the headlights are too dim to see properly in the dark, there could also be a problem with the alternator and the charging system in the vehicle.