# Chevy Mysterious Brake Light Problem



## hsousa1997 (Dec 6, 2019)

Hello All. Im having an issue ive never seen before with my 2006 Chevy 3500 Duramax dump truck. With the truck off, the brake lights are off as normal and if I step on the brake pedal with the truck off, the lights come on. But the strange thing is, with the key in the "run" position or with the truck on, the brake lights come on and stay on, and if I step on the pedal, nothing happens, the lights dont get brigher or anything. They just stay on. No matter what position the switch is on the dashboard, this happens. I recently replaced the brake booster, master cylinder and all the brake lines on the truck. Everything, including the lights for about a week until this started happening My assumption is perhaps a faulty brake light switch/relay or a fuse. Im wondering if anyone has had this weird problem before I start messing with things. Some insight would be great. Thank you


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## Mr.Markus (Jan 7, 2010)

Does your cruise control work?
There is a switch on the pedal that can get stuck periodically as it gets older. Change it out.


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## Randall Ave (Oct 29, 2014)

Mr.Markus said:


> Does your cruise control work?
> There is a switch on the pedal that can get stuck periodically as it gets older. Change it out.


This.


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## Avalanche 2500 (Dec 31, 2015)

Just a thought, W/ truck on ck. inspect your trailer switch harness > does it feel warm if so, there is a short so replace harness the wires will look fried/ corroded. Or like Mr. Markus said ck. brake light switch


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## cwren2472 (Aug 15, 2014)

Randall Ave said:


> This.


But he said the pedal works normally in the off position- if the stop light switch had power in the off position and was stuck, wouldnt the lights stay on all the time?


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## cwren2472 (Aug 15, 2014)

Does the truck have a trailer brake controller? If the manual lever was stuck, that is usually switched with the ignition and would cause the lights to stay on


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## 1olddogtwo (Aug 6, 2007)

Multifunction switch is my bet.


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## Mr.Markus (Jan 7, 2010)

On mine it was hit and miss, some applications it would stick and others it wouldnt. I never noticed the brake lights on at all until my cruise stopped working and i started trouble shooting. Once i figured out it was the switch i wondered how long i had been driving with my brake lights lit up..like that old guy that drives with his right foot on the throttle and left foot rested on the brake.


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## hsousa1997 (Dec 6, 2019)

Thank you all for your advice. I havent had time to work on it this week, tommorow Im going to stat working on it. My assumption from the get go is it was the brake light switch. I have yet to see if the if the cruise control works. Also my truck does not have a trailer brake contoller. Ill replace the switch anyway, and after I do that ill report back.


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## SilverPine (Dec 7, 2018)

Very good chance it's the brake switch. Mine did the same as well as randomly flicker. Happened to two different trucks. Chevys have very odd electrical problems!


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## EWSplow (Dec 4, 2012)

1olddogtwo said:


> Multifunction switch is my bet.


GEM module? I've never had a problem, but have heard stories of windows going up and down on their own.


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## 1olddogtwo (Aug 6, 2007)

EWSplow said:


> GEM module? I've never had a problem, but have heard stories of windows going up and down on their own.


Actually the multifunction switch is located in your turn signal lever.

Besides operating your turn signal, it split signal/power to the 3rd brake light on the roof. This is how the 3rd light stays solid when turn signals are on.


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## EWSplow (Dec 4, 2012)

1olddogtwo said:


> Actually the multifunction switch is located in your turn signal lever.
> 
> Besides operating your turn signal, it split signal/power to the 3rd brake light on the roof. This is how the 3rd light stays solid when turn signals are on.


Gotcha. I'm not much of a mechanic, especially when it comes to electrical issues.


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## hsousa1997 (Dec 6, 2019)

I replaced the brake light switch and still having the same problem. I did not try to see if the cruise control works. I did however hook up my trailer, and it's doing the same thing as the truck. Just to clarify, my truck does not have power windows or door locks. Some more advice on what else it might be would be appreciated


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## cwren2472 (Aug 15, 2014)

hsousa1997 said:


> I replaced the brake light switch and still having the same problem. I did not try to see if the cruise control works. I did however hook up my trailer, and it's doing the same thing as the truck. Just to clarify, my truck does not have power windows or door locks. Some more advice on what else it might be would be appreciated


Does the 3rd brake light stay on also?


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## Philbilly2 (Aug 25, 2007)

Didn't think a dump had a 3rd light. 

lights for the dump box are quite often pulled from trailer circuit not the truck trail light circuit.

I would be curious if this is in the wiring rats nest in the back of the truck or on the BCM.

I will place my bet on that you are having a grounding issue in the rats nest.

Do me a favor. Try your four ways. Do they work with the truck off? When you start the truck, do they work then? After you apply the brake and your lights stay lit, do they work then?


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## cwren2472 (Aug 15, 2014)

Philbilly2 said:


> Didn't think a dump had a 3rd light.


The cab doesn't have a third brake light?


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## cwren2472 (Aug 15, 2014)

hsousa1997 said:


> I replaced the brake light switch and still having the same problem. I did not try to see if the cruise control works. I did however hook up my trailer, and it's doing the same thing as the truck. Just to clarify, my truck does not have power windows or door locks. Some more advice on what else it might be would be appreciated


For giggles, try pulling the fuse on the right that's circled and see if anything changes.


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## Philbilly2 (Aug 25, 2007)

cwren2472 said:


> The cab doesn't have a third brake light?


Every one that I have had has had a blank filler. No brake lite.


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## Avalanche 2500 (Dec 31, 2015)

@ the brake light swicth there should be a rod unhook it adjust, turn 2 x's to the left, reconnect ck. the lights ?


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## Randall Ave (Oct 29, 2014)

Start pulling fuses out one at a time and see if it goes out, I would start with the turn signal fuse.


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## Philbilly2 (Aug 25, 2007)

Randall Ave said:


> Start pulling fuses out one at a time and see if it goes out, I would start with the turn signal fuse.


Which one? The truck or trailer turn signal fuse?


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## hsousa1997 (Dec 6, 2019)

My truck does not have a third brake light, just has the blank cover. The four ways work fine with the truck off, on, and even whey applying the brakes. I also have adjusted the rod at the brake light switch and that did nothing.


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## hsousa1997 (Dec 6, 2019)

I have the Rubbolite 8002 & 8003 lights with the Dorman 923-012 tail light circuit board if that helps


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## Philbilly2 (Aug 25, 2007)

hsousa1997 said:


> I have the Rubbolite 8002 & 8003 lights with the Dorman 923-012 tail light circuit board if that helps


The fact that you knew those numbers makes me wonder...

Have you recently done something with this stuff that makes you know those numbers?


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## hsousa1997 (Dec 6, 2019)

No no, I just looked the numbers up.


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## cwren2472 (Aug 15, 2014)

hsousa1997 said:


> No no, I just looked the numbers up.


Did you happen to pull the fuse I suggest earlier?


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## Philbilly2 (Aug 25, 2007)

cwren2472 said:


> Did you happen to pull the fuse I suggest earlier?


you thinking back feed threw the 12v trailer plug wiring? dosen't that stay on even with the key off?


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## cwren2472 (Aug 15, 2014)

Philbilly2 said:


> you thinking back feed threw the 12v trailer plug wiring? dosen't that stay on even with the key off?


_Usually_ if it is part of the factory tow package it's switched with the ignition so it's only live when the truck is on - that way a trailer with a light on inside doesn't inadvertently kill the truck.

And yes - if the brake lights work normal with the ignition off, then something somewhere is backfeeding to the lights that is only switched on with the ignition.


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## hsousa1997 (Dec 6, 2019)

i haven't tried that yet. When I do I'll let you know what happens


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## Philbilly2 (Aug 25, 2007)

cwren2472 said:


> _Usually_ if it is part of the factory tow package it's switched with the ignition so it's only live when the truck is on - that way a trailer with a light on inside doesn't inadvertently kill truck.
> 
> And yes - if the brake lights work normal with the ignition off, then something somewhere is backfeeding to the lights that is only switched on with the ignition.


Hunh... I don't remember my GMT-900 frames if the plug was constant or not, but I know that the K2XX (2015-2019 2500/3500) it is always live.

If it is switched on the GMT-900 frame, that is a good thought.


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## Randall Ave (Oct 29, 2014)

Philbilly2 said:


> Which one? The truck or trailer turn signal fuse?


I am just guessing, but possibly something in the Multi function switch is crossed. I would start there. He could un plug the trailer socket and see if that turns them off.


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## hsousa1997 (Dec 6, 2019)

Hello All, I still havent figured out the issuse with my brake lights.I dont know if this was happening before, my brake lights are still acting the same but also when I step on the brakes with the truck off, the parking lights and the roof lights come on. Im certian that isnt normal, and perhaps its related to my brake light issues. Some insight would great


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## Philbilly2 (Aug 25, 2007)

Have you done anything suggested?

I still sounds like you have a dead short between circuits in the wiring.


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## Aerospace Eng (Mar 3, 2015)

hsousa1997 said:


> Hello All, I still havent figured out the issuse with my brake lights.I dont know if this was happening before, my brake lights are still acting the same but also when I step on the brakes with the truck off, the parking lights and the roof lights come on. Im certian that isnt normal, and perhaps its related to my brake light issues. Some insight would great


I think it may be a bad ground for the lights. When you depress the brake and the brake light switch activates, the voltage can't find its normal ground, and so runs backward through the other lights that share the common ground.

My guess is that when you start the truck, some light (e.g. daytime running lights, clearance lights) that shares the same ground powers back through the brake lights.


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## Avalanche 2500 (Dec 31, 2015)

Start here w/ wire brush, sandpaper, 13 m socket


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## Philbilly2 (Aug 25, 2007)

Aerospace Eng said:


> I think it may be a bad ground for the lights. When you depress the brake and the brake light switch activates, the voltage can't find its normal ground, and so runs backward through the other lights that share the common ground.


My that sounds familiar...



Philbilly2 said:


> I will place my bet on that you are having a grounding issue in the rats nest.


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## cwren2472 (Aug 15, 2014)

Philbilly2 said:


> My that sounds familiar...


Pfft. Might as well give @Randall Ave credit too then for telling every single person ever to check their grounds. Should the OP get out his DVOM?


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## Philbilly2 (Aug 25, 2007)

cwren2472 said:


> Pfft. Might as well give @Randall Ave credit too then for telling every single person ever to check their grounds. Should the OP get out his DVOM?


I always laugh at the number of times through out the years that I plowed even to now where people will call me with problems and I ask them if they checked all their grounds.

After they tell me they had check them, I tell them call me back after they check them again... typically never needed to call me again for that issue.

He will not need a voltage meter... He just needs to go back to the rats nest at the back of the truck and pull the loom off and find the broken ground.


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## Randall Ave (Oct 29, 2014)

cwren2472 said:


> Pfft. Might as well give @Randall Ave credit too then for telling every single person ever to check their grounds. Should the OP get out his DVOM?


My ears was a burnen, what'd I do wrong now?


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## cwren2472 (Aug 15, 2014)

Randall Ave said:


> My ears was a burnen, what'd I do wrong now?


Nothing buddy, you're good.


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## Randall Ave (Oct 29, 2014)

I don't have time for shenanagens, I'm busy annoying people with stupid 6.0 engine pics.

We really need some snow.


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## Avalanche 2500 (Dec 31, 2015)

hsousa1997, any luck > results w/ troubleshooting brake light issue ? Us P/S guys like results, Come back ?


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## hsousa1997 (Dec 6, 2019)

Hello All. First I hope everyone is safe and healthy amidst the current pandemic. I figured I’d provide an update with the brake lights. Haven’t had much time to dig into it lately, but now that the weather is getting warmer I’d like to get back into it. First I still have been driving the truck. My issue was the brake lights don’t “get brighter” with the truck on. They stay “steady on” with the truck on. With the truck off they work fine. I didn’t notice it beforehand, but the brake lights work fine with the headlights/all other truck lights off, wether the truck is on or off. Just with the lights on they don’t work right. Cleaned up all the grounds, checked all the fuses, replaced the brake light switch and the bulbs. So a refresher of old advice or some new advice would be fantastic. Thanks


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## thelettuceman (Nov 23, 2010)

So a refresher of old advice or some new advice would be fantastic. 
New Advice: Your truck has COVID 19 .... I hope you don't


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## Randall Ave (Oct 29, 2014)

Sounds almost like the bulbs are wired in backwards.


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