Have 2003 chevy avalanche tail lights out but brake light works. I changed the bulb twice and itdidnt fix it. This problem is on left side only(drivers side).

The left and right tail and brake light assemblies have separate fuses. The left side is a 5A fuse #3 in the underhood fuse box. Check that out first

The tail light fuse is under the rear seat on the drivers side.

Have you tried swapping the bulb from the other side see if that works If not check for power and ground at the tail lamp circuit that is inoperative. Also take a good look at the connector(s) make sure there is no corrosion in the terminals.

check the light checking unit power for light go through this to the bulbs tell you when a bulb is out. center light is not on this circuit.

Next thing to do would be to check the bulb sockets to see if the terminals are bent/broken/corroded.

Fast flashing dash signals mean there is a bulb issue-DEFINATELY!

is the bulb good, is the socket good, I would swap the left and right bulbs. then go from there

The printed circuit board that the bulbs push into needs replacement. Any autoparts store will have it. It just screws into tailight assembly & attaches to wiring harness.

Replace the tail light circuit board. They are sold at most auto parts stores.

Solution to your problem ... 1- I purchased from 1aauto.com a pair of Circuit Boards for my Chevy Venture 2003 for 85.00 $ ..free shipping 2 - I Installed them both , all lights now were not working at all. So I checked them and they were all burned ...So I purchased new ones ....Everything was working fine now but now my signal lights were not working left and right .....Checked the fuse box next to the passenger side door .... It was burned . Changed the fuse / Signals are working fine now ....All is good I just did this yesterday evening August 12, 2008 Conclusion ..Change everything going forward so you do not need to run around like I did from one store to another!

1. Circuit Board : New
2. Bulbs : New
3. Fuses : New

Thank you