I have a 1999 Pontiac firebird that when I turn headlights on only one is bright and the other three comes on dim when I have them on low beam. When I put them on brights only one side lights up and other side completely go off.

replace your headlamp bulbs

I replaced both low and hi beam bulbs and it still does the same thing. Another suggestions?

check your ground wires

Could you tell me where these grounds exist and locations. Do you have any pics? Thank you much for your time.

follow the wiring harness around the headlight assemblies, sometimes easier said than done, a meter when troubleshooting can help as well, should see a black wire being fastened to body (or supposed to fastened to body)

Can’t believe I actually found someone with the EXACT same problem I’ve got… and on a recent post! Have you figured anything out with this? If nothing else I may as well start troubleshooting in a different area than what you’ve already looked at…

A little time with a multimeter ruled out bulbs and grounds for mine. Obviously it's time to start tracing wires; was just really hoping to find some brilliant insight that might eliminate the need to... Anyone??

then there is a short somewhere, good luck, check the switch and wires to dimmer in steering column

I have the same problem going on. I have check the connectors and cleaned the ground wire connectors to the frame. Nothing worked. Any more ideas?

Has anyone found the problem to this yet. Mine do the same thing if I unplug the harness and plug them back up they will work OK for a little bit

my 99 just started doing this. anyone get this issue resolved?

My 98 just started doing this. Driver low is on, other three glow with 1.5 volts. When I unplug the other low, it goes off and the tow glowing high go off too. Tried different low beam bulbs, same result. Have not tried unplugging both high beams yet, will try that soon. Looks like a few people had this issue, has anyone solved it?

Solved! The headlight motor wiring harness includes the wires that go to the headlights. There are five wires, ground is the black one on the end. When I used a multimeter on the headlight connection, I was getting 12v, but when plug the light and it does not come on. My ground was not connecting properly enough, so when there was a demand on the positive the negative wasn't strong enough to handle the return. I disconnected the 5 way headlight actuator motor wire harness and the side that goes to the car wiring is basically the female side of the connection. I used a small pic, like a screwdriver but sharp bent point on the end, to pic behind the female connection. In essence, prying it outward. Connected the harness, and boom, got my low beams back. Tested high beams and they work as they should.