Brake lights work in the opposite fashion, when you brake they turn off and when you are not hitting the brake they are on

Tiny
BBALLER902100
  • MEMBER
  • 2006 MINI COOPER S
  • 1.6L
  • 4 CYL
  • 2WD
  • MANUAL
  • 100,000 MILES
Car had issues with water in the wiring connectors just under the fuse panel. Cut our connectors and soldered all wires back together. I was left with 4 extras that basically were not being used. My brake lights work in the opposite fashion, when you brake they turn off and when you are not hitting the brake they are on. I have replaced the brake switch, bulbs and took the BCM/BCI apart no water ever on that side of the vehicle. All other lights are working, the only other issues I am having are the trunk motor does not pop open. I also do not know if these mins have a button for the trunk to pop open? The brake light is a scary issue that I would like to get fixed. Thank you all for your help this has been a journey.
Sunday, October 6th, 2019 AT 5:05 PM

16 Replies

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

This almost doesn't make sense because the circuit is closed when you press the brake allowing power to travel. With that, the only thing that comes to mind is if you have the ground and power send reversed somehow and it's allowing the continuous flow of power until the circuit is closed. Now that I said it, that doesn't make sense. Lol

Lets start with this. I attached two pics. The first one shows the wiring at the switch. The power is supplied to the switch and is sent through the switch when the circuit is closed to a few places. One is the general module which redistributes power to the brake lights, the other is the ABS unit. See pic 1

Picture 2 shows power from the switch to the general module and then how it's distributed to the tail lights. I have arrows pointing in the directions of power flow.

Take a look at the attached pics and let me know if specifically, one of the wires was switched at the switch. Note that the first pic shows wire color and pin number in the plug.

Also, the last pic is of the switch. Could you have reversed how the switch attaches causing it to work in reverse?

Let me know what you find.

Joe
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Monday, October 7th, 2019 AT 7:56 PM
Tiny
BBALLER902100
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First off I want to thank you for taking the time to try to assist me. My brake light switch has 4 wires that come out of it. I replaced the switch with a “standard” brand and was direct plug and play. I am not going to lie I am having a hard time following your photos and making complete sense with them, largely because I am not electrically inclined. I have attached some photos to show how I connected the wires and I am not sure what to try next.
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Tuesday, October 8th, 2019 AT 5:32 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Welcome back:

You are very welcome. I just hope I am helpful.

Is there any way the plug may have been put on in reverse? Also, if you can, upload the pics you have. Something is reversed, either in the mechanics portion or something that changed polarity (meaning the power is running in the opposite direction).

I have to be honest, no matter how I look at this problem, it doesn't make sense. The switch itself is either closed or open, meaning power either can or can't go through it. Regardless of the polarity (flow of power) if the switch is open, power can't go through it.

With that in mind, I think you got a bad switch. There is always power to the brake light switch. However, for the power to continue to the lights, the switch has to be closed (meaning it has to complete the circuit) so power can continue regardless of direction. In this case, you have power all the time until the switch is closed. I think something is bad in the switch itself. That is just a theory at this point, but if the part is under warranty, I would remove it and have it replaced with a new one to see if that changes things. The only other thing that makes any sense to me is if it was somehow wired wrong.

Tell me this. If you disconnect the connector at the brake light switch, do the lights go off?

Let me know if you have questions and if I can get the pics you have.

Take care,
Joe
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Tuesday, October 8th, 2019 AT 5:50 PM
Tiny
BBALLER902100
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Joe. When the lights are on from just inserting the key when I remove the switch is does nothing. If I press the pedal down (the lights are off) and then unplug the switch the lights turn back on. It’s like the switch is doing exactly the opposite of what it is suppose to be doing. The switch is brand new from amazon and is under warranty in which I can ask for a replacement. The connector into the switch can only go in one way so I couldn’t have messed that up. There are two brown/black wires that I swapped to see if something was flipped and nothing changed. Do you happen to live in Michigan? I really just want this to be over with.
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Tuesday, October 8th, 2019 AT 5:58 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Welcome back:

I wish I was closer, but I'm in PA. I really feel the switch is bad. Nothing else makes sense to me. Get one at a local parts store and plug it in (you don't have to mount it) and see if it makes a difference.

It totally understand your frustration. Hang in there. We get it figured out one way or another.

Joe
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Tuesday, October 8th, 2019 AT 6:21 PM
Tiny
BBALLER902100
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Ordered a new plug from a different manufacture from amazon. This one is a beck Arney the other was a standard. I’ll let you know on Thursday evening. Thanks again
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Tuesday, October 8th, 2019 AT 6:35 PM
Tiny
JACOBANDNICKOLAS
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Welcome back:

Did you order the plug or the switch?

Joe
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Tuesday, October 8th, 2019 AT 8:40 PM
Tiny
BBALLER902100
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Switch. Is there a plug too?
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Wednesday, October 9th, 2019 AT 8:54 AM
Tiny
BBALLER902100
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I tested the old switch that I replaced and it’s really the same thing. I don’t think it’s the switch any more. I test for voltage on the 4 terminals. First one when key in ignition shows about 5.2, next 11.2, 0, 12.
When the brake is pressed 5.2, 0, 0, 12.
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Wednesday, October 9th, 2019 AT 3:17 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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No, I asked about the plug that goes on switch thinking that was what you meant. As far as the voltage, I need to know which wires have which power. Did you install the new switch yet?

Joe
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Thursday, October 10th, 2019 AT 6:25 PM
Tiny
BBALLER902100
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Above I shared what voltages each wire has. The new switch did not change anything.
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Friday, October 11th, 2019 AT 8:36 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Welcome back:

Can you tell me which wires each voltage came from? I need that.
Let me know,

Joe
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Saturday, October 12th, 2019 AT 7:19 PM
Tiny
RODCHERO86
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Hi, I have an 2004 Mini base model. My brake lights won't turn on at all. I have 12 volts going in on there purple wire the brown has 0 ground but the other 2 wires only have 1.3v. I've changed the switch twice already. Can somebody please help?
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Friday, May 7th, 2021 AT 1:28 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

This could be indicating a faulty General Control Module. The two wires (one on each side) need to have 12v. The left wire is black/green and the right is black/blue. Those are the wires for the brake lights. The purple wire is for the left side only and controls a fog light in that light assembly.

What I need you to do is check for power out at the control module. It is located on the right side of the vehicle, behind the kick panel.

I attached four pictures below. This is the entire wiring schematic for the exterior lighting system. I had to cut the two pics in half to make them readable, so that's why there are four. I did overlap them so you can follow from one to the next. Additionally, I highlighted the wires in question. When you go to the module, check to see if 12v is there. If it isn't, chances are the module is bad.

Here is a link you may find helpful:

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

Since you have 12v to the fog lamp, that tells me the control module is receiving the correct amount of power. So, you could have corrosion at the connection, a poor connection due to connector pin damage, or the module may have failed internally.

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

Take care,

Joe

See pics below.
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Friday, May 7th, 2021 AT 7:07 PM
Tiny
NIKOLAY YURUKOV
  • MEMBER
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Hey guys.

I found a solution to the backward working brake light switch.

The switch itself has a female socket inside that the wired male socket that comes out from the car (the one that is beyond the brake pedal) plugs into.

This female socket can be pushed out from the switch by using a small "straight" screwdriver and just needs to be flipped. If you look at the sides of the switch you can find where to push as there are 2 small canals on each side.

I just registered to share this since I spent many hours fixing this. I bought a new switch and it worked backward (brake lights were always on and when pressing the brake pedal they shut off). At first, I thought I broke it by plugging and unplugging it over 50 times in one day and playing with it. The above-mentioned socket just came off from the switch and before smashing it into the ground I thought I'd. Try to flip it and it worked. Ended up it's been inserted incorrectly.

I hope this helps.
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+1
Friday, August 11th, 2023 AT 2:32 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
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Excellent addition to this thread! Please feel free to use 2CarPros anytime!
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Saturday, August 12th, 2023 AT 9:06 AM

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