Brake light help

walkerlutz · August 15, 2015

Hi! Hoping someone on here might be able to help me. I've tried searching everywhere and can't find an answer to my problem. My Brake lights don't work but my third one on the cab does work. They both went out at the same time.

I've replaced the rear junction box but there isn't even power going into it(I tested the end of the plug coming from the cab.

I traced the wires into the engine compartment but didn't find any breaks.

I checked all the fuses in the cab and engine compartment (I think... not really sure which ones affect the brake lights.)

I checked the switch at the brake pedal and there is power going in and power out when depressed.

Any help would be greatly appreciated. Also does anyone know what order the power flows through the fuse boxes? maybe battery to engine fuse box to brake switch to cab fuse box to rear junction box to lights?

GLSierra13 · August 16, 2015

Does the power out from the brake lamp switch go to the BCM? On my '13 Sierra, the brake lights don't work unless the key is on. I assume that means the BCM controls the lights. Maybe that could be a clue on yours, too. (???)

walkerlutz · August 16, 2015

Thanks for the suggestion but I don't think its the BCM. The brake lights work whenever the brake is depressed regardless of whether the vehicle is on or the key is out of the ignition.

walkerlutz · August 16, 2015

Also one of my turn signals in the rear works so I know its not the bulb. The other turn signal flashes twice as fast and works in the front but not the rear

BlackZ71Silverado · August 16, 2015

Also one of my turn signals in the rear works so I know its not the bulb. The other turn signal flashes twice as fast and works in the front but not the rear

Check the bulbs if that's the case. There are two elements inside the bulb, one for brakes, one for turn signal. If the turn signals work but the brake lights don't it's probably the bulbs. The fast flashing is also a sign that a bulb is bad.

walkerlutz · August 16, 2015

Thanks

BlackZ71Silverado

I replaced the bulbs and that fixed the turn signal lights but the lower brake lights still don't work... I have no clue what it could be

BlackZ71Silverado · August 17, 2015

Did you change those bulbs also?

The turn signals and brakes use the same 3047 bulb but there are actually 2 elements inside the bulb, one for brake, one for turn signal. If replacing the bulbs doesn't work, I don't know what it would be. For them to just stop working all of a sudden is strange to me.

Are you sure ALL of the fuses marked for "lights" are good? If a fuse is bad the brake lights won't work.

If the fuses are all good, there has to be an electrical issue somewhere.

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