Brake light issue

BRAKECHECK

MEMBER
2004 HYUNDAI ELANTRA
4 CYL
2WD
AUTOMATIC
200,000 MILES

Greetings and well wishes.

Recently purchase the car listed above used (no cruise control).

Brake lights work properly when the running lights or headlights are off.

Brake lights illuminate brightly when the running lights or headlights are on as if the pedal is being pressed. There is no change in the brightness when the pedal is pressed while the lights are on.

Because I had recently bought the car, I checked all blade fuses.

I replaced both of the 1157's in the brake light socket.

I replaced the brake light switch up behind the pedal.

Short of removing the trunk liner, I see no evidence of a trailer harness. Nothing hanging or tucked away.

I have yet to replace an amber running light that's out on the front quarter panel and the '3rd' brake light bulb.

I have some experience, changing brakes, oil and such. I can follow detailed instructions.

So, where to next, the turn signal/headlight switch on the column? Something else?

Thank you, ahead of time.

~Rob V

5 Replies

KASEKENNY

MECHANIC
18,907 POSTS

Sounds like you have one of two issues. Either you have a short in the brake lamp circuit or someone tried to repair the wiring and ran your brake lights to the wrong circuit. So I would take the brake assembly out and start testing for shorts to one another.

The way you do that is check for resistance between the stop lamp wire to each of the other wires in the connector. They should all be open circuits.

I suspect some has wired this wrong so when that checks out, check for continuity on the stop lamp circuit from the assembly to the junction block. You do this by putting one meter lead in the wiring terminal at the brake lamp connector at the tail light and the other in the junction block where I circled it. You will need to use a jumper wire as the meter leads are not long enough. Put the meter on resistance/ohms/continuity and then press the brake pedal. You should have resistance or continuity. I suspect you will not. Which means someone wired the brake circuit to the headlamp/taillamp circuit.

Let me know what questions you have.

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

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

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Friday, November 27th, 2020 AT 2:32 PM

BRAKECHECK

MEMBER
3 POSTS

KASEKENNY1

Thank you for your reply. Additional thanks for the links and diagram. I will get ahold of a multimeter tomorrow, follow your advice the best I can and post results and any questions that come up.

RV

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Friday, November 27th, 2020 AT 7:05 PM

KASEKENNY

MECHANIC
18,907 POSTS

Sounds great. We are here if you have other questions. Let us know what you find. Thanks

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Saturday, November 28th, 2020 AT 5:22 PM

BRAKECHECK

MEMBER
3 POSTS

Kasekenny1

Greetings and well wishes.

Ground!

After weeks of driving during the daytime only, I finally enlisted help in following your suggestion.

Before getting started with the multimeter, we noticed a socket in the taillight assembly on one side was partially cracked, allowing some 'wiggle room' for the bulb. After finding out that the socket alone isn't sold at the local AutoZone. Dealer or pic a part only for the whole assembly. I decided to put it back together and run it awhile longer, as is.

That decision paid off!

As we buttoned it back up and began replacing the fuse and junction box covers, my helper noticed that the point of contact where the negative battery cable was grounded to the vehicle needed a good cleaning. Not as if that were my problem, just that it needed attention. He did that while I put the tail light assemblies back in.

I checked the lights again.

Well, sir, the poor ground was it. Problem solved. The running lights and brake lights work as they should. Additionally, the intermittent Check Engine light is but a memory. The airbag light went out. I wasn't even aware that the door key triggered all 4 electric door locks until they suddenly came to life. It ran 'okay' before, but now seems to idle a bit smoother, too.

Go figure.

Thank you, again.

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Thursday, January 21st, 2021 AT 9:28 PM

KASEKENNY

MECHANIC
18,907 POSTS

That is great! Poor grounds always seem to be the cause of the odd issues. Great job and thanks for coming back to update us. I am sure that info will help others. Thanks for using 2CarPros. Talk to you next time.