Brake lights comes on with taillight but does not function as brake light

1994 CHEVROLET SILVERADO
250,000 MILES • V8 • 4WD • AUTOMATIC
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DIRTYDBAGGER
  • MEMBER
  • 1 POST
Hello everyone, and thanks in advance for any and all help. On my truck listed above k1500 when I turn my lights on the driver side brake light on the drivers side comes on with the tail light and therefore brake lights are not functioning properly. I fixed part of this problem by replacing the whole assembly due to hearing that the boards are known to go out on these trucks. It didn't stop the brake light being illuminated when taillights were on but they did brighten up when brakes were pressed. I also heard the trailer lights if installed wrong could cause similar issues, so I disconnected them to no avail. Any and all suggestions are greatly appreciated.
Mar 17, 2019 at 7:13 AM
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JACOBANDNICKOLAS
  • ✓Experienced Mechanic
  • 110,246 POSTS
Hi and thanks for using 2CarPros.

If your brake light turns on with the lights, you have to have a short to power to that light. Have you carefully checked the wiring? Also, have you checked the grounds? A bad ground can cause power to back feed through other circuits to make contact and this is the type if thing that can happen.

With that in mind, first, inspect the pins in the connector to the light assembly to make sure noting is bent or damaged. Next, check the wiring as far as you can for cuts or damage to an insulator that can cause a short.

Last, I want you to check the grounds to and the main ground under the vehicle responsible for all rear lighting. I attached a picture of the ground and rear lighting. It indicates locations of the grounds. Check those.

Here are a few links you may find helpful:

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

https://www.2carpros.com/articles/how-to-use-a-voltmeter

https://www.2carpros.com/articles/how-to-check-wiring

Let me know what you find or if you have other questions.

Take care,
Joe

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Mar 17, 2019 at 1:04 PM
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