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2006 chevy trailblazer_ls_ext
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59 Posts
Discussion Starter #1
Hello everyone,

May need some electrical assistance. Just noticed my brake lights dont work. The third brake light on top of the tailgate hatch works, just not the two on the left and right rear.

I checked the #12 fuse in the hood box and it is good.
I checked the #34 and #51 fuses in the rear box under the seat and they look good.

I think the bulbs are fine because they all worked except for the brake light feature. I cant seem to remember if the brake lights are lit up on the top set of red lights or the bottom set of red lights?

When I turn my headlights on, the top set stay lit red. When I trun my emergency signal on, the bottom set blink red. Just nothing when I hit the brake. So I am assuming the bulbs are fine.

Any suggestions on what to check next? I read about a tail light circuit board but dont know where or what that is or how to replace it.

Any help would be appreciated. Just my luck and seven days outside my warranty I notice this.

Trouble
 

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2003 isuzu ascender
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115 Posts
Probably need 2 new TOP bulbs. Since some OE bulbs seem to not last so long. Hey, it will only cost you $5-6 for a set at most auto stores, its cheaper than a REAR ENDER. Most people rarely check their lights and they usually fail ONE AT A TIME. If they still don't work, then its likely one of the brake light switches under the dash at the pedal "bar". My bet is on the bulbs!:D
 

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2006 chevy trailblazer_ss_ls
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7,988 Posts
:iagree:

The top bulb is tail/brake light. Since both are out and the fuses are good, I'd say it's probably the bulbs. It's pretty unlikely that both of your boards are bad.:m2:
 

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2003 chevy trailblazer_ls
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5,267 Posts
if you remove the entire brake light assembly- the tailight circuit board is the long plastic piece that the bulbs get pushed into.
remove the assembly and look into the bulbs contact points... sometimes those turn black and lose connectivity. or the bulbs plastic melts.
 

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2006 chevy trailblazer_ls_ext
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59 Posts
Discussion Starter #6
We are all masters of the obvious. Rule #1. Start with the cheapest part first.

It was the bulbs. I thought the bulbs where fine because with the headlights turned on, the top red lights were also on. Apparently, the bulbs are like three way bulbs. I guess the brighter brake light part was blown out.


I still havent replaced my brakes yet from my other post but with your guys responses from before Im sure I will do fine.

:thx
 

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2002 gmc envoy_slt
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561 Posts
Im having the same problem but its definitley not the bulbs because i just replaced them and i still have the problem. I checked some fuses under the back seat but im not sure which is the right one. Does anyone know the fuses that control the rear brake light function only? I also had a leaking sunroof recently do you think it could of shorted something?
 

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2004 gmc
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26,181 Posts
Fuse 34 in the rear, cleverly labeled VEH STOP.

Fuse 16 in the rear is the for the Center High Mounted Stop Lamp (CHMSL)

Both of them get their power by way of the stop lamp switch on the brake pedal, which in turn is fed by fuse 12 under the HOOD.

So if you lose ALL brake lights, it could be the switch or fuse 12.
 

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2006 gmc envoy_sle
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1,614 Posts
Does your cruise control work? if it doesn't it is tied in with you stop lamps. ( had this happen whan trying to to put LEDs in the brake lights)
So that fuse would be open. not sure which fuse it would be.
 

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2002 chevy trailblazer_lt
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1 Posts
chuck2053

Had only third brake light operation. Changed bulbs and checked brake fuse with no luck. Finally went online to trailvoy and found VEH STOP fuse #15 could be the problem. IT WAS!!! THANKS A LOT you guys.
 

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Similar problem, been working on it for 2 weeks. No brake lights. I have changed fuses that where good anyway, changed bulbs that where good (but made them work for about 2 days and stopped working again. Changed bulbs a second time with no improvement), changed brake light switch twice (worked for about 4 days and they stopped working again so I changed it again with no luck, resistance is good on both switches the the bad one away), checked resistance on circuite boards. I had the switch connector wired to a toggle switch so I could drive to the parts store but now I can't even get that to work. I recently changed the alternator and have been fighting electrical issues with the OBD port, the oil pressure sending unit, the instrument cluster going out intermittently, the headlights won't go off sometimes, now the battery has taken a crap but an buying a new one today. I can take the key out of the ignition when it's running so I'm wondering if the ignition lock cylinder had anything to do with it or the ignition switch. Also I just changed the transmission interlock switch on the side of the transmission so I'm wondering if the selenoid needs replaced now. I hear it clicking when I lightly jiggle the wires on the brake light switch so I'm thinking also maybe that connector is bad. Especially since I can't hardwire it like I did last time. I swear this thing has a gremlin in it that knows I'm in love with my truck and is trying to make me go broke. I also just replaced the upper and lower ball joints on both sides, the inner and outer tie rod ends on both sides, the hub assemblies in both sides and now one is out again but is still under warranty. That along with the starter, water pump, alternator and front brakes. Now it needs the back brakes. If I keep going I'm going to
have a brand new 15 year old truck. This is what I get for letting my ex wife drive it while we where married. It was originally hers but she did no maintenance on it and I took it when she left. So I'm having to pay for 5 years of no maintenance on a used vehicle. All I have done for 2 years is constantly diagnose problems and fix them. And will continue to do so.

Soo, any ideas on the brake lights? HELP GUYS! I GOTTA FIX MY BABY.
 

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There's a longer story concerning a wrong jack crank that was jammed into the place where the jack is stored. The handle ripped out the wires, shorted others and I had no brake lights on both sides and no tail lights on the left side.

After repairing the wires and replacing the fuses, still had no response from the left circuit board.

It turns out that there was a pin in the Molex that had rusted and broken off inside the female side and it just jammed the connections to a tiny point of contact and that wasn't enough to carry the bulb load.

Sometimes the obvious isn't the answer - and this one defied my standard of "Never suspect zebras when you hear hoof-beats". This time it was zebras! But the best action is to start from the device/part that isn't working, and go to the source, eliminating the electrical circuit/pathway and connex along the way.
 

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I replaced my battery and still have no juice at the brake lights. After replacing the switch twice within a week I remembered that if I lightly jiggle the wires in the brake light switch connector I can hear the shift interlock selenoid on the shift lever clicking. So I'm thinking the connector is bad. I bought one from the jump yard today since no one carries it. I can at least use this one to verify that is the issue. I checked continuity and resistance on each line and used a 9 bolt battery to power each wire and checked voltage at the terminal pin and got 9.36 volts on each one with a little 9 volt battery. That was just for my mind to verify that there was a good connection at each terminal pin before I cut out one I think is bad and put this one it's in. If that fixes it I will order a new one and swap it out. Just not until I see it fixes the problem.

Anyone know where I can get a wiring diagram that lists the wiring color code at the brake light switch connector on my 03' Trailblazer? And does the color code at the switch carry through to the circuit board connector? And where is the ground for the brake lights located as well as how do I access the wiring harness in the cargo area so I can check all these wires.
 

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AutoZone will have a very concise and accurate wiring diagram with color codes and descriptions. You can print them out and make your own book like I did.

The book I made for my 2005 EXT/TB has 58 pages, single-sided.
 

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I had to repair the brake lights on my wife's Astro Van.

The CHMSL worked OK but like you, the bulbs in the tail lamps wouldn't light up.

What I found was a lot of resistance in the taillight ground circuit due to corrosion.

What seems to have happened was that the CHMSL, being LEDs, didn't require the current necessary like the tungsten filiment bulbs in the taillights did.

I cleaned the ground and everything came back to WNL.

.... just sayin'......
 

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Thanks, I'm waiting on a friend to drop off his Chilton's manual, we both have the same trailblazer, so I can see where the grounds are and how to access the wiring harness in the cargo area so I can inspect the wiring. I also have a new accessory socket to install back there. With 250k+ she is showing her age. But my baby isn't good anywhere but back into surgery. I'm thinking about having a sign made for my driveway that labels the slot I park in as
"O.R. 1" since my truck is the one always being worked on. And another for the slot my daughter Parks in as "Recovery Room 1".
 

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It appears the previous owners pressed the #12 fuse in so hard that it broke free from the fuse box. And from what I understand from the Chilton's manual the #34 fuse under the rest seat is powered by that #12 fuse. The #34 fuse has no power and the #12 has to have pressure applied and pushed a little too the right to have power on both sides. So I'm thinking the next step is pull the fuse box and try to get that #12 fuse socket secured and supplied with power the way it's supposed to be. That way it can power the #34 fuse in the back that is labeled "VEH STOP". If it can't be secured then I can always solder on another piece of wire and add an inline fuse to take the place of the one in the fuse box or jump it over to a fuse socket that isn't being used. As long as it's a secure connection and properly insulated and clearly marked and labeled it shouldn't be a issue.

Any advice or issues I need to address that I haven't listed already? I do electrical in houses ask the time. I realize DC is quite different, but I have a working knowledge and all the proper tools. But opening a fuse box can be quite intimidating if you haven't been there before.
 

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AutoZone will have a very concise and accurate wiring diagram with color codes and descriptions. You can print them out and make your own book like I did.

The book I made for my 2005 EXT/TB has 58 pages, single-sided.
Do you happen to have the link to that or the search term for the diagram on Auto zones website. I can't find anything. I bought the Chilton's manual but there are no color codes and it doesn't show the location of the grounds. The grounds can be ram e to a splice pack and then 1 wire ran from there to the ground or it can be ran directly to the ground. So having the location of the splice pack or the actual grounding point and the color codes would be awesome!
 

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2004 GMC Envoy SLT 4.2
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Do you happen to have the link to that or the search term for the diagram on Auto zones website. I can't find anything. I bought the Chilton's manual but there are no color codes and it doesn't show the location of the grounds. The grounds can be ram e to a splice pack and then 1 wire ran from there to the ground or it can be ran directly to the ground. So having the location of the splice pack or the actual grounding point and the color codes would be awesome!
I guess you didn't look very hard .
 
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