I have a 2002 Trailblazer. I have changed the

Check wiring at the headlamp connection. There something loose.

under dash above brake pedel the charm box the relay is be side it

i had a simular problem, if you haven't already check the fueses. try changing the light bulbs.

It can be faulty low beam lamp or its connection issue for low beam lamps.

There are few solved helps links with proper solution to troubleshoot these issues.I suggest you to refer the links below.Click the link:----
Passenger side low beam out?

http://repairhelpcenter.blogspot.com/2012/01/passenger-side-low-beam-out.html

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Low beam HID light goes out? http://schematicsdiagram.blogspot.com/2012/01/low-beam-hid-light-goes-out.html
----------2007 Dodge Caliber: Low Beam Headlight Not working http://technoanswers.blogspot.in/2012/06/2007-dodge-caliber-low-beam-headlight.html
-------------Chevy Tahoe: Low Beam Lamps are not working? http://technoanswers.blogspot.in/2012/04/chevy-tahoe-low-beam-lamps-are-not.html
----------2001 Chevrolet Tahoe: Both Low Beam Lamps Not Working? http://technoanswers.blogspot.in/2012/04/2001-chevrolet-tahoe-both-low-beam.html
--------------2002 Toyota Tacoma: Low Beams not working? http://technoanswers.blogspot.in/2012/04/2002-toyota-tacoma-low-beams-not.html
-----------Low beam headlights Modification? http://schematicsdiagram.blogspot.in/2012/04/low-beam-headlights-modification.html
-----------DRL and Low beams not working? http://schematicsdiagram.blogspot.in/2012/04/drl-and-low-beams-not-working.html
-----------These will help.Thanks.

For the drivers side, reach down by your alternator and over behind the headlight. You'll feel a 3" round rubber boot. Slip this off and now you can remove the light bulb.

Passengers- Remove the top of the air cleaner, at that point you'll have complete access to the rubber boot and bulb.

FACE THE VEHICLE SO THAT BATTERY IS ON YOUR RIGHT;
2.REMOVE THE BLACK PLASTIC PIECE THAT RUNS OVER RADIATOR BETWEEN HOOD LATCH AND FAN. IT IS ABOUT 53 1/2" LONG AND HOLDS THE HOOD PROP CLIP. (3 PLASTIC PUSH RETAINERS & 2 SHEET METAL SCREWS);
3.REMOVE THE GRILL ASSEMBLY UNDERNEATH THE PIECE IN STEP 2 BY PUSHING DOWN FIRMLY ON 4 RETAINER CLIPS WHICH RUN ALONG THE TOP. USE A WIDE SLOT SCREWDRIVER. PULL UP GENTLY ON GRILL ASSEMBLY. IT WILL POP OUT. THE GRILL ASSEMBLY EXTENDS UNDER EACH HEADLIGHT ASSEMBLY (HA) AND IT DISPLAYS THE CHEVROLET LOGO IN THE MIDDLE. MY GRILL ASSEMBLY POPPED OUT EASILY AND ALL THE OTHER RETAINER CLIPS ON THE BOTTOM AND BENEATH AND TO THE SIDE OF HA WERE AUTOMATICALLY RELEASED WITHOUT ANY FUSS;
4.ON TOP OF HA SEE ONE TAB (ABOUT 1" LONG)ON THE RIGHT SIDE AND ONE ON THE LEFT (THE ONE ON L IS CLOSER TO THE FENDER);
5.PULLUPWARDDIRECTION ON TABS. THEY WILL SLIDE UPWARD A COUPLE OF INCHES AND WILL RELEASE THE HA WHICH YOU CAN THEN PULL OUT TOWARDS YOU;
6.AT BACK OF THE HA, REMOVE 2 ROUND RUBBER CAPS (ABOUT 4" IN DIAMETER)--ONE FOR LOW BEAM--ONE FOR HIGH. REVEAL BULBS. UNSNAP THE WIRE HARNESS FROM BULB BASE AND TURN BULB 1/4 TURN CLOCKWISE (REMEMBER YOU ARE FACING THE TRUCK)
7.REPLACE BULB(S). #9006 BULB IS GRAY-BASE, FOR HIGH BEAM ON OUTSIDE. #9005 IS BLACK-BASE, LOW BEAM TO INSIDE OF HIGH BEAM.
CHANGING HIGH AND LOW AND REASSEMBLY TOOK ABOUT HALF HOUR. GOOD LUCK. ALTERNATIVE: IF YOU ARE REPLACING THE PASSENGERSIDE HEADLIGHT JUST REMOVE THE AIR FILTER COVER AND PULL PLUG OUR FROM BEHIND HEADLIGHT AND REPLACE. BE CAREFUL HANDLING LIGHT BULB. TO CHANGE THE ONE ON THE DRIVER'S SIDE JUST REACH IN FRONT OF THE BATTERY TO ACCESS THE PLUG AND HEADLILGHT. TOOK ABOUT 5 MINUTES. ENJOY YOU TRAILBLAZER, GREAT TRUCK.

both low beam ights wont work on my VW 2000 beetle I have checked the fuses, bulbs, and relays what could be the problem

Bulbs fitted incorrectly.Or your adjustment is out.of line.Adjust them behind the lamp.good luck.

There is more than one relay I know but make sure your bulbs are good I HAVE seen this happen more than once.. low beams can go at once.. and still have hi beams check this first please .. Jerry

All you have to do is find the "round rubber cover" on the back of the headlamp, pry it out with a flathead screwdriver and the lamp is right there.
To remove the headlamp assembly on a Trailblazer, remove the plastic panel that covers the hood latch assembly.
Take the cover for the air filter in order to get to the low beam cover.
Take the 3 screws out of the air filter cover and remove. You will then be able to get to the back of the low beam lamp. The high beam is reachable without this hassle.