Brake lights stay on

Tiny
ROOKIESTANG
  • MEMBER
  • 2010 FORD MUSTANG
  • 3.7L
  • V6
  • 2WD
  • AUTOMATIC
  • 200,000 MILES
Recently my car when turned off had the brake lights stay on.
-I did change the brake light switch and still stayed on
-I disconnected the switch it still stayed on.
-I pulled fuse 2(Good fuse) "BOO" and they go off, played with the hazard lights and they blink with fuse 2 removed and messing with my multi-switch to see if after plugging fuse 2 back in to see if it works (still on).
-With fuse 2 plugged in (lights still on) and pressing on hazard lights switch the lights blink but the upper middle brake light still on.
-Once in a while when I removed the car battery connectors and have fuse 2 removed and put them back in it works like normal for a short time until I drive the car.
-I've been scratching my head for a bit and trying to follow these wires: Looking at all the switches that control the brake lights from my car locking/opening mechanism, brake light switch, hazard light switch, flashers, light switch when driving at night, I did not check them all since I did not want to mess anything more up.

Side note: When driving around my Trac Off light comes on at random and sometimes I can't turn it off, not sure if that is relevant or not, because it is right next to the hazard light button and the trunk button.
Thursday, August 1st, 2019 AT 7:53 AM

6 Replies

Tiny
ROOKIESTANG
  • MEMBER
  • 4 POSTS
-Also did pull back on the brake pedal, still, brake lights are on.
-When the car works after having fuse and car battery removed and reconnected.
1. Brake light switch works, just saying.
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Thursday, August 1st, 2019 AT 8:14 PM
Tiny
SCGRANTURISMO
  • MECHANIC
  • 4,897 POSTS
Hello,

This could be an internal short to power in your vehicle's Body Control Module B (BCM)(B) which is located in the right rear of the luggage compartment. It is after fuse #2, so unplugging the fuse would cause a break in the circuit as you can see in the wiring diagram of your vehicle's external lighting. I have included in the diagrams down below for you as well as a diagram of the BCU B's location. Please go through these guides and get back to us with what you are able to find out.

Thanks,
Alex
2Carpros
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Friday, August 2nd, 2019 AT 4:28 AM
Tiny
ROOKIESTANG
  • MEMBER
  • 4 POSTS
Followed the diagrams, after looking everything over and driving for a bit after going to the car wash. I noticed the lights come back on and the Trac Off light come on once in a while. I noticed my Cowl had water sloshing around and built up, the water went into the Cabin filter, and moistening the passenger side floor next to fuse box, would this be the internal short? I have some pictures and not sure if I found the culprit to the brake lights staying on and the trac light coming on once in a while. If this is the problem will electrician wd-40 work on fixing this and new electrical tape for the wiring since most of it is unraveling on its own and covered in a oily substance? Or will this have to be taken care of by a ford service location?
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Sunday, August 4th, 2019 AT 7:51 PM
Tiny
ROOKIESTANG
  • MEMBER
  • 4 POSTS
For attached images that did not load.
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Sunday, August 4th, 2019 AT 7:52 PM
Tiny
SCGRANTURISMO
  • MECHANIC
  • 4,897 POSTS
Hello again,

If it isn't the problem, then it soon will be. Okay, the electrical connectors can be cleaned up yourself. CRC makes a special cleaner for electrical connectors and it should be available at any auto parts store. It is called QD electronic cleaner and again, it is manufactured by CRC. That should clean up the corrosion the is producing the unwanted resistance on these circuits. Next you should probably get a tube of Dielectric Grease and put on these connectors. It is conductive grease that will help to weatherproof them. Finally, you need to fix the original problem, which is the water collecting and getting into the cabin. Wherever it is getting in at needs to repaired, or else this will happen all over again. Please keep us informed as to how things progress.

Thanks,
Alex
2CarPros
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Monday, August 5th, 2019 AT 1:17 AM
Tiny
CALEB136
  • MEMBER
  • 1 POST
Oh my goodness! Thanks so much to y’all! I have a 2010 Mustang Convertible V6 with the same exact problem. I noticed water dripping down behind the glove box, which turned out to be from a clogged drain in the Cab air filter as well. It flooded my floorboard with about 2 gallons of water. My brakes have been flashing since. I tried everything you mentioned before I found this thread, I replaced the fuse and cleaned the whole fuse box with fine electronics cleaner. I just now singled out the problem to the wiring harness that deals with TC, ABS, and brake lights apparently! I have worked on this all day, and just sat down out of frustration. Y’all solved my problem! Thanks!
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Saturday, February 13th, 2021 AT 6:06 PM

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