Only my brights work - 2003 Toyota Avalon

You have a bad ground wire in the headlight wire harness

check the bulb sockets , ck your ground

If the right flasher is working and the left flasher is not, that should be a burned out light bulb, either front or rear. (outside)
If you will wait until it is dark, it is easier to diagnose.
After dark, turn on the right turn signal, then look carefully at the brightness of the front and the brightness of the rear turn signal. Now, turn on the left, and again observe the brightness of each. One of the bulbs should be out, or not as bright as the other side. That is the bulb you will need to replace.

Your circuit lights may be bright or dim according to how your electrical system was set up. It may dim when lights are off and get bright when lights are on. ------------------------------------------------------------------------------------------
Car Diagnostic Tools

check your fuse box. High beams (brights) usually have their own fuse. Otherwise it could be a problem with your switch (i assume its one of the arms behind your steering wheel) buyt i would pull the fuse first. Refer to the diagram for your specific car. fuses are cheap and you can tell theyre blown when you pull them out (a break in the fuse)

Brights won't work,bright indicator won't come on 2005 Highlander

your dimmer switch is faulty. There's a catch inside the switch that keeps the switch actuated when you pull it back and release it, and that's not happening. You will have to replace the switch to get your brights working correctly. Good luck, and hope you get it fixed quickly.

Dimmer switch is going bad. If you rapid fire the switch they will switch from bright to dim or dim to bright. replace the colum switch.

I had the same problem. The solution is simple; the ignition switch needs to be replaced. This is an easy do-it-yourself project. Here are instructions:
http://forums.vwvortex.com/zerothread?id=2532481
Check for a switch on ebay, they are about $15. After 10 years they wear out.