Question about 1994 GMC Sierra

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Third brake light works but two on rear dont.

I have a 1994 GMC half ton extended cab and my third brake light is working but the rear two do not. I have changed the turn signal switch and the brake light switch. I have rear parking lights as well as turn signals, and my hazards work. When you turned the flashers on before and pushed the brake pedal they would stop flashing they do not now and only brake light that is working is the third breaklight. I am at a loss noone seems to know what the problem could be... HELP

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  • chrislvidaur May 24, 2009

    Ok well after alot of scratching my head and alot of help from my dad we got it. As I said i had replaced the turn signal switch and brakelight switch with still no luck. As it would turn out there is a relay under the hood that the power must run through before it ever makes it to the turn signal switch. The third brake light was working because it apparently runs directly from the brakelight switch, but the back two run through the relay and then through the turn signal switch. All in all the relay was bad, a 28 dollar relay but I now have brake lights in the rear which is a plus. Thanks and I hope that this will help someone else in the future.

  • Anonymous May 24, 2009

    Thanks for the posting. My son and I have been trying to figure out the EXACT same problem on a 1998 chevy p/u. Haven't bought the relay yet, but after reading you posting, I pretty sure it will work. Thanks again for sharing. By the way, the brake switch on our truck is a bear to remove, let alone change.

  • Anonymous May 25, 2009

    Where exactly is this relay located?

  • gerry bissi May 11, 2010

    must be the splice where it splits off to the high mount lamp and the tail lamp brake lights.

  • blair Aug 14, 2012

    does anyone have a solution for this one?



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  • 57 Answers

Have you replaced the bulbs?

Posted on May 22, 2009

  • Bennie Kennedy May 25, 2009

    cool, glad it's fixed! I try not to get too involved with the comments. You never know how mec. inclined people are.

  • blair Aug 14, 2012

    I have this problem too, but i dont see anywhere on here the solutioin to it. please help



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