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Old 06-24-2010, 10:35 PM
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Exclamation 2001 headlights not working

Hi all, i am new here and could really use some help

I have had 4 different S series trucks and i have a decent amount of knowledge about them but this has be stumped.

My 2001 Blazer's headlights do not work at night. During the day the DRL lights work fine. Turn signal, marker and brake lamps also work fine. However at night the regular headlights do not work at all. I have tried removing/replacing the DRL relay and related fuses but i get nothing. Even if you try to turn them on with the manual switch you get nothing. as i said before all other external lights on the truck work fine.

Another little issue to throw into the mix is that is problem is intermittent.

If anyone has any input on this i would really appreciate it. I have owned S series trucks for the past 10 years and i thought i knew just about all there is know know about them until this problem came along.

Thanks in advance!!
Anthony
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Old 07-04-2010, 02:04 AM
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i have the same problem (2002 s-10 blazer)....maybe just coincidence but when i hit the kickplate under steering wheel the lights would come on...also when i would switch lights to or from highbeams all lights would go out...all fuses are good, all other lights are on...now my lights wont come on at all, light control switch is working also (dimmer and interior cutoff switch works) i think its a short, someone told me it might be the brain in my alarm is no good, im gonna take it to the mechanic but if anyone knows anything about this i would appreciate it
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Old 07-04-2010, 06:35 AM
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To the OP, locate and replace the headlight grounding relay.

Below you will find a schematic of your headlights. I believe this is the same as all '98+ non-zr2 models:


KayRock, if you have aftermarket equipment on your truck that ties into those systems somehow, the diagnosis of your problem gets quite a bit more involved. I would usually disconnect the aftermarket alarm and return the wiring to stock. If the problems go away, the aftermarket stuff was at fault. If they do not, then the standard diagnostic procedures apply.
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Old 07-09-2010, 05:20 PM
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tried everything myself with no end....tried new swith new dimmer nothing.....took it to a shop and after a few hours found in a wire relay/junction box under steering column to the left just above the emergency brake, well when we took it apart, female detaches from male when we detached it where the ground wire went in it was burned out messed with it lights came on still working on it (box needs replacement) does anyone know what the name of this box is (has about 30 wires in it
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Old 07-20-2010, 12:30 AM
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Did you ever get this resolved, or figured out the name of that box, or found schematics to it, or anything? I'm having the exact same problem, have looked everywhere, googled everything, with no luck. I already replaced all the bulbs, the relays under the hood, redid the grounds at the radiator support, cleaned the contacts on the multifunction switch, and a million other things, before noticing the clicking coming from that damn box under the dash, every time the lights flicker out (which can sometimes happen as much as 10-20 times a minute, very annoying and unsafe!). Please advise, thx!

[email protected]

PS - I've also been looking for that box in a junkyard, with no luck. It seems specific to 2001-2002 model years?

Last edited by CompTechMike; 07-20-2010 at 12:32 AM.
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Old 07-20-2010, 03:22 AM
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i took the car to a mechanic and after 4 hours of work...tried new headlight switch, new dimmer...didnt work...the tech tested power to the headlight and there was power but both terminal positive and ground were both giving power so the mechanic said there is a bad ground somewhere in the car....they almost couldnt figure it out but under the dash (remove kick plate on left side by drivers shin just below the emergency brake is a white box with about 15wires in it it seperates one half of the box is male the half that faces driver is female...im not sure of the mane but its some kind of junction and in that junction is 1 ground wire when the mechanic touched the box lights went on..i told him whatever you just did fixed it when he examined the box one of the wires was burnt...whalla it was the ground...he couldnt loop around the box and dint know if he could find the part but as a temporary fix he brushed off the burnt terminal and pull the wire through to a tighter non burnt part and that did it....its not a perminent fix....(i need to find out name of the part to replace) but it did the job...my problem was also intermittent but after a while became permanent so i would look into it...i knew before hand that there was a short somewhere cause my lights would flicker(dash, head/tail, and even the temp/compass lights) but if i kicked the part where that box was lights would come on so my only advise is if you have a 2002 blazer unscrew the kick plate locate that box unscrew it and see if any wires are burnt
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Old 07-20-2010, 03:25 AM
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you could also test the body command module (bcm) through the obd outlet...but that click is the headlights trying to go on
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Old 07-20-2010, 08:43 PM
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Default I solved my issue

This is how I fixed mine. There is a relay center, that is not listed in any manual that I have seen. It is located on the driver side of the truck sorta behind the gauge cluster. The best way to get to it is from under the dash on the driver side. It has about 8 or 9 relays, their only function is to control the auto interior and exterior lights. I replaced ALL of the relays. And now I have no problems.

As a side note, I have a very good knowledge of 12vdc automotive electronics and after replacing these relays and fixing my truck I bench tested the relays I took out, none of them tested bad.

P.s. I also had the same issue with all the pins on the head lamp plugs showing 12v+. Now, after a few weeks I still have no problems. Also this relay center is NOT common to all s-series trucks w/ auto head lamps.

Last edited by sonic2552; 07-20-2010 at 08:46 PM.
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Old 07-21-2010, 07:58 AM
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This is exactly the same problem I'm having (even down to the pins at the headlamps showing weird voltages, although redoing all the grounds at the radiator support seems to have helped that a lot), thanks guys! I'm going to see what I can find for relays at the auto parts store, really wish I had a freaking diagram showing *what to ask for* when I go in and purchase said relays (thanks, GM :-/ ), and will also check for burned/damaged wires. This is so much better than paying $150 for the multifunction switch! (which even the dealer said I should replace, when I paid them $30 to help diagnose the issue)

I'll post again and let you know how it goes.
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Old 07-21-2010, 09:37 AM
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Oldie, but goodie --> Headlights don't work - help! found by searching for "body+relay+block" with an author of "swartlkk"

In the newer trucks, there may be nothing behind that cover. In this case, the body relay block is up under the dash as many of you have found.

There is only one relay in the body relay block that has anything to do with the headlights and that is the headlight grounding relay. This relay supplies the ground to the headlights allowing for series mode (full brightness) and takes it away when in DRL or parallel mode (half brightness).
 
 
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