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Brake light issue

Discussion in 'GM Electrical Tech' started by 994x4, Mar 31, 2014.

  1. 994x4

    994x4 New Member

    Hello I have a 99 Sierra 4x4 that I just bought and just realized the brake lights do not work. So far I have checked/replaced fuses, bulbs, brake switch, circuit board, etc. I am at a loss as to what the cause could be. 3rd brake light does not work either. The turn signals, park lights, and backup lights work just fine. I tried to check grounds off the tail lights and all the wiring seems to be going back to the circuit board so I don't know where else to look. Any help or places to start looking will be greatly appreciated. Thank you.
  2. RayVoy

    RayVoy Active Member 2 Years 1000 Posts

    You need a volt meter to track it down.

    Sounds like you have changed everything, but here is a quick overview.

    12v power through a fuse, to brake light switch, at this point the circuit usually splits, one lead going to the center light, the other going to the rear taillights. Both of these circuits will be fuses.

    Usually:
    - if all three are dead, the problem is the first fuse, or the switch.
    - if the center light is out, it is usually a bulb, or the fuse for that circuit (does your truck have a bulb, or is it an LED assembly?)
    - if the two in the tails are out, it is usually two bad bulbs, the fuse, or a broken wire.


    You tell me you have checked/replace the fuses and the bulbs, please tell me how you did this?
  3. 994x4

    994x4 New Member

    I checked both fuses, one under hood labeled "STP LTS" 10A.
    checked fuse in dash labeled "TAIL LTS" 10A
    replaced both tail bulbs 3157
    replaced tail light circuit board
    removed and checked the brake switch, took it apart and didn't see anything broke or anything like that

    all 3 stop lights are inoperable.
    non led.
  4. RayVoy

    RayVoy Active Member 2 Years 1000 Posts

    Under the hood, you have a fuse marked STOP/HAZ
    In the dash, you have a fuse marked #1 which is stop CHMSL and haz

    Here is a copy of your owner's manual: http://www.gm.ca/media/owners/manuals/1999_GMC_Sierra_Manual_en_CA.pdf
    Check page 6-71 and 6-74.

    Ok, the switch looks like it is good; but, does it operate when the pedal is pushed, maybe it's out of adjustment.

    Ya know, you've changed a lot of parts; for about $10 you could have purchased a volt meter and with a little practice, followed the voltage to the problem.

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