Just to replace the bulb, open the hood, there should be a small plastic panel above the head lites, remove it, the bulb with the holder twist out. Then plug the new bulb in and replace. If you need to replace the whole headlite, the unit is available for about $ 45.00 and that includes 55 w bulbs, 60w for the high's, new lens, with adjusters. Due to age the plastic yellows and the lites are not as bright as before, therefor, the new units are a good deal. Takes about an hour to change both sides. Just have to remove the clips from the inside.
As the climate change bulbs
The headlamp bulbs on a 1996 Acura TL are installed from the engine bay. Find the housing located in the front of the vehicle. Disconnect the bulbs and replace them with new units.
open trunk, remove the 4 wing nuts, remove the casing from the outside. Bulbs are in there.
burnt bulbs, switch or fuse.
If you can't access the bulbs take the light assy off and turn the bulbs counterclockwise to remove them
On a 2004 envoy, open the hood and on the top of the headlight assy there are two tabs that you pull up allowing you to pull the headlamp assy forward and access the the bulbs. These are halogen bulbs so remember to wear gloves when handling the bulbs.
Check the bulbs, the fuse then the brake light switch.
3. 2 for the main lites, and 1 in the center
http://www.baby-benz.com/portal/lighting/bulb-replacement.html
there is two rods that go through the housing from the top. turn them to unlock and pull up and out then the whole assembly comes out and you can change the bulbs.
pull up on the 2 tabs that hold it to the housing. then siply twist the bulbs out of their sockets
You probably have a bulb out. Remember, the rear has two blinker bulbs