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2002 GMC Sierra 1500 Z-71 Brake Lights Failed

absinthminded

By absinthminded
in Ask A GM Technician

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absinthminded Enthusiast

absinthminded

Posted
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Gents, I have a 02 Sierra 1500 4x4 with 190k, 5.3L. A few months back the cruise control started to work intermittently. Then eventually, It failed all together. Being that I know little about electrical systems and Its an old truck, I dismissed it. Recently, I decided that I wanted my cruise control back and I started reading about the issues others had and how to repair. I read that the cruise control and the break lights are connected and that the cruise will not work if the stop lamps have failed.

I started with my usual method of trouble shooting, look it up online, throw parts at it, cheap and easy first. I swapped in a delco stop lamp switch and a doorman dist block. It didn't help. Then I realized that when I start the truck with the remote start and then step on the break pedal, It shuts the truck off. I believe the switch to be fine.

  • Cruise button will not light the green indicator on the gauge cluster,
  • Stop lamps do not work
  • original stop lamp switch appears to be functional
  • fuses both under hood and on the side of the dash are good
  • 3rd brake light works, now that I replaced the bulbs
  • tail, reverse, turn signals, and hazzards all work. I believe the distribution block to be fine. (I even tried swapping it with a doorman unit)
  • I replaced tail lamp bulbs
  • all signals to my trailer plug are good except stop lamps

20151228_145230_zpss7rswerd.jpg

 

Nice!

20151228_171526_zpsr6a6gkoy.jpg

 

20151228_170319_zps2azhri0l.jpg

20151228_170251_zpsdnca9ch3.jpg

20151228_170147_zpsgcm5h8e3.jpg

 

So, in my digging around I found a purple wire plugged in under the dash. First I noticed the corrosion and then I saw it was burnt. I unplugged It and saw that the socket was also burnt. Then I pulled the trim back and discovered that wires that go the 3rd break light have been tapped into. I believe the burnt purple wire runs to the rear defrost. I never use it. I don't really want to replace that block, plug, and wire harness $.

 

I have a test light but not a volt meter. I can purchase or borrow one if need be. I think either I have a broken wire in the harness under the truck or maybe the turn signal stalk/switch is bad.

 

Thanks in advance for any help.

absinthminded Enthusiast

absinthminded

Posted
  • Author
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I just picked up a multimeter today from H.D. I will see what I can do. I need to test voltage at the stop light switch on the pedal. Then I want to jumper direct to the break light harness as close to the switch as possible and see if i can get them to light. Eliminating the possibility a bad wire running all the way back to the tails.

Doug_Scott Senior Enthusiast

Doug_Scott

Posted
Posted

You should find out where the wires go that were tapped into the third brake light. Do not really think that is an issue, but, since the power to brake lights only appears when brakes are applied, it is odd to have something tapped into it for power.

 

What is a "doorman dist block"

 

If your truck uses the same bulbs/filament for both brake and turn signals, then the signal switch/flasher is involved in the brake lights as well. If your truck has a signal flasher unit with more than 3 wires, then the flasher could be causing the brake lights to not work. On vehicles with a 2 or 3 wire flasher can, the signal switch in the column can cause brake lights to not work(on vehicles with combined brake/signal bulbs).

 

Since the 3rd brake light works properly, I am pretty sure you can safely assume the brake light switch is working. If the signals and brake lights use the same bulb/filament in the rear, and the signals work, you can safely assume wiring, bulbs, and sockets are good as well.

 

If I am reading your post correctly, you have not had brake lights for a few months now, and no one ever told you?

 

One of the stupidest things GM ever did was to stop the brake lights from working with the key turned off. Used to be I could check brake lights when I got in the car before starting the engine by looking in the mirror with my foot on the brake and see the lights on the wall. Now, I have to turn the key on and that turns the parking lights on as well, so the wall is already reflecting those lights.

absinthminded Enthusiast

absinthminded

Posted
  • Author
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The distribution block is located under the bed on the frame. It has 4 wire harness plugged into it. One is the feed from the front and then distributes to the tail light assemblies, trailer lights and license plate lights. I tried a replacement part from Doorman (thats the aftermarket brand).

I'm gonna head back to the garage and see what I can come up with.

I'm having a difficult time finding a wire diagram for the stop light switch, and the wiring in the back. upfitter didn't seem to be much help.

absinthminded Enthusiast

absinthminded

Posted
  • Author
Posted

So I retraced all my steps. I decided to reference the owners manual while checking fuses. A bit embarrassing but after all that work, I found a bad fuse.I probably wouldn't have checked it if I didn't know what the stop light switch was.

20151229_204734_zps1o3g1nnm.jpg

That one right there.

Doug_Scott Senior Enthusiast

Doug_Scott

Posted
Posted

What I used to do when I was looking for an electrical issue was to use a test light to test all fuses. The switch to blade type fuses made it very easy to test. Did not bother looking at the map, just tested all of them. Sometimes the label does not list all the circuits that fuse covers.

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