# Gremlins in the Brake Light **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [October 13, 2014, 11:05pm UTC](https://community.cartalk.com/t/gremlins-in-the-brake-light/87645 "2014-10-13T23:05:09Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Terry829](https://avatars.discourse-cdn.com/v4/letter/t/8e8cbc/32.png) [@Terry829](https://community.cartalk.com/u/Terry829)\ **Post date:** [October 13, 2014, 11:05pm UTC](https://community.cartalk.com/t/gremlins-in-the-brake-light/87645/1 "2014-10-13T23:05:09Z")
Hey all. I’m driving a 2010 Hyundai Sonata and just recently one of my brake lights has been acting up. Everything works perfectly fine as long as the head lights are off; however with the head lights on, when I depress the brake pedal my driver’s side tail/brake light goes out. The center brake light and passenger side brake light work just fine regardless of the head lights being on or off. With the headlights off, all the brake lights operate normally when the pedal is depressed. Any thoughts? Thanks! ---
**Author:** ![BustedKnuckles](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/bustedknuckles/32/25_2.png) [@BustedKnuckles](https://community.cartalk.com/u/BustedKnuckles)\ **Post date:** [October 14, 2014, 5:57am UTC](https://community.cartalk.com/t/gremlins-in-the-brake-light/87645/2 "2014-10-14T05:57:47Z")
Maybe a bad ground at the driver’s side light connection. With the headlights off, the brake lights can ground through the tail light circuit and to another light that is grounded on that circuit. But, with the headlights on and the tail light circuit is powered, it negates that ground circuit and nothing lights. ---
**Author:** ![Barkydog](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/barkydog/32/2470_2.png) [@Barkydog](https://community.cartalk.com/u/Barkydog)\ **Post date:** [October 14, 2014, 6:25am UTC](https://community.cartalk.com/t/gremlins-in-the-brake-light/87645/3 "2014-10-14T06:25:32Z")
It could be as simple as a bad bulb Try a new driver side bulb first. ---
**Author:** ![SteveCBT](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/stevecbt/32/3192_2.png) [@SteveCBT](https://community.cartalk.com/u/SteveCBT)\ **Post date:** [October 14, 2014, 6:26am UTC](https://community.cartalk.com/t/gremlins-in-the-brake-light/87645/4 "2014-10-14T06:26:44Z")
Check your brake light bulbs, years ago I had a dual filament bulb go out and the broken filament ended up attaching itself to the good filament. When I used the turn signal, power went backwards through the attached filament with strange lights working and caused me all sorts of headaches trying to figure it out. ---
**Author:** ![Cougar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/cougar/32/21348_2.png) [@Cougar](https://community.cartalk.com/u/Cougar)\ **Post date:** [October 14, 2014, 9:32am UTC](https://community.cartalk.com/t/gremlins-in-the-brake-light/87645/5 "2014-10-14T09:32:38Z")
I agree with @BustedKnuckles advice. The grounding for the rear light having the trouble needs to be looked at. The headlights use much more current than the brake light does so rear light doesn’t get the proper current it needs to work because of the voltage drop across the ground system when the headlights are on. When the Hdlights are off there is no voltage drop to rob the power needed by rear light. Check and clean all the grounds under the hood. ---
**Author:** ![Terry829](https://avatars.discourse-cdn.com/v4/letter/t/8e8cbc/32.png) [@Terry829](https://community.cartalk.com/u/Terry829)\ **Post date:** [October 14, 2014, 3:10pm UTC](https://community.cartalk.com/t/gremlins-in-the-brake-light/87645/6 "2014-10-14T15:10:20Z")
Thanks all! I’ll definitely check the grounds, and failing that change some bulbs and see where that leaves me. ---
**Author:** ![knfenimore](https://avatars.discourse-cdn.com/v4/letter/k/9fc348/32.png) [@knfenimore](https://community.cartalk.com/u/knfenimore)\ **Post date:** [October 14, 2014, 10:31pm UTC](https://community.cartalk.com/t/gremlins-in-the-brake-light/87645/7 "2014-10-14T22:31:16Z")
The tail light ground is in the trunk G32 in the pic. I would start with replacing the bulb.