the bulbs themselves...and or the dimmer/light switch....read up on bulb replacement, then since that's the cheapest, change any burnt bulbs and see if any other bulbs are loose in their sockets...good luck..
Everyone should have a manual for their vehicle, and a professional shop manual should be available at your local library for diagnostic procedures etc, just make copies of the right pages, as they are usually REFERENCE only...read up and good luck :)
short somewhere in the wiring or bulbs might be loose
Probably a loose connection in the wiring or the bulb socket.
The tail lights are on a separate wiring than the blinker/brake lights. Look for a blown fuse or a broken/loose wire.
Cracked wiring in the harness. But first make sure fuses are not loose in their holders.
Could be a wiring problem. Could also be loose connections, which I doubt, but hey.. anything's possible, right? I'm voting for wiring.
The fuel sending unit is sticking, or the wiring to the gauge is loose. These are the two most common causes of an erratic gauge.
Check to see if you have a blown fuse. This is often the case. Also you may try pulling the rear lights out and inspecting them for any damage or loose wiring.
this tells you is a simple wiring problem.most likely a loose wire from the third light to the other lights.(third lights provides the power to the other lights)
The switch for your lights is probably going bad or is dirty, you may also have a loose wire or connector. Find some way to spray WD40 inside the dash dimmer switch may help a lot.
If the headlights on the 2004 GMC Envoy are not working, there could be a loose connection somewhere. If all of the other lights are working, it is most likely not a fuse that has blown. Double check the wiring to see if there is a loose connection.
Assuming that you have checked the fuses, look for a loose connection in the wiring harness. I believe that there is a connector in the trunk area that may have come loose.
I found this on my 1997 Silverado and found the connection from the wiring harness to the back OS the switch itself was loose, I could wigle it arouns and make the lights come back on.