Brake lights not working properly

Tiny
ZACHARY MAY
  • MEMBER
  • 2014 KIA OPTIMA
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 55,000 MILES
The third brake light (middle) comes on but the two side brake lights do not.
All the rear bulbs are working as I tested all of them (turning night time lights
on, turning on hazards, etc.). But the side rear lights do not illuminate more
when I press the brakes.
I could not figure out which fuses are apart of the side brakes using the
owners manual.
Also whenever I put the car in cruise control, the brakes still turn off the
cruise control settings.

Any tips would be helpful. Thank you for the time.

Because the cruise control turns off when I brake and the third brake light comes on, I was not sure if that means the brake switch is working correctly.
Saturday, August 17th, 2019 AT 12:03 PM

3 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Welcome to 2CarPros.

The fuse is a 15 amp fuse in the under hood fuse box and a 10 amp in the vehicle. See pic 3. However, since the high mounted light works and the cruise control works (great test by the way), it isn't a fuse issue. The high mounted light gets power from the same place as the others.

With that in mind, I attached a portion from a wiring schematic. The pink wire on the left supplies power to the brake lights. Now, I circled a joint connection where the wires converge. It is behind the left kick panel (next to your left foot when in the car). You need to check the condition of that connection to make sure nothing is loose, corroded, or damaged. If you follow the green wires from the connection, you will see that power goes to the high mounted light and both brake lights on the sides of the vehicle. So if one gets power, they all should.

So, the only other thing that I can see that would affect both side lights and not the 3rd is ground location. If ground is lost, but if that was the case, none of the lights would work. If you look at pic 2 it shows that ground for both sides and a different one for the third brake light. If you question that at all, confirm the back up lights work. If they do, the ground should be good.

Check those things first and let me know what you find. Here are a few links you may find helpful:

https://www.2carpros.com/articles/how-a-car-fuse-works

https://www.2carpros.com/articles/how-to-check-a-car-fuse

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

I hope this is helpful. Let me know what you find or if you have other questions.

Take care,
Joe
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Saturday, August 17th, 2019 AT 6:21 PM
Tiny
ZACHARY MAY
  • MEMBER
  • 2 POSTS
I'm dumb. Just for background, I have a heavy electrical background but know almost nothing about cars.

After agreeing with your assessment from the wiring diagrams and checking my reverse lights, I realized that I was in an impossible scenario. So I started back at square one and realized that I was looking at the wrong bulbs. I was looking at the bulbs in the trunk hatch of the car and not the lights in the side compartment of the trunk.
Both bulbs were burnt out and I replaced them. Everything works fine. Thank you for helping me out and making me realize that I am dumb :D
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Monday, August 19th, 2019 AT 7:30 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Welcome back:

LOL that is an easy mistake. If you don't have a helper, it is easy to pick the wrong ones. Regardless, I'm glad you got it working. You have no idea how often things like this happen so no worries. My favorite is, "I have no low beams. They stopped working:" What happened is one burned out before without the driver knowing and then the second one did the same. Then I get the argument that they couldn't have burned out at the same time. LOL

Take care and let me know if you need anything in the future.

Joe
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Monday, August 19th, 2019 AT 7:07 PM

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