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Discussion Starter #1
I’ve got a 2004 Mini Cooper 1.6 convertible as my first car and the brake lights didn’t work so I ordered a new switch and this sorted the problem for about 4 seconds and now it’s all backwards as the lights are constantly on then when I press the brake they turn off etc any ideas as to how to resolve this would be much appreciated
 

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You haven’t got the wires round the wrong way have you?
Brake light switches are a simple switch where a contact is made (or broken) when pedal pressure is removed from the switch. As there is only 1 contact internally, it doesn't matter which way round you connect the cables.
 

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As the left and right lights go to separate earth points it seems unlikely that earths for the light clusters are your problem. I can't see how they would cause that issue anyway.
 

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It appears BMW went a bit nutty when they decided on what kind of switch to fit and went with a hall effect switch...


...instead of the traditional type I described above.

Also they have changed the circuit between the switch and the BCU a few times so it is possible you may have a switch that operates differently.

This is the wiring diagram for your brake light switch:-


This is the diagram for cars built prior to Aug 2003 (note the diode between brake and BCU):-

 

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I'm dubious about there being any wiring faults as you have the ability to switch the brakes on and off with the switch. That tells me that the BCU is receiving the signal and controlling voltage on the output wire.
 

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Discussion Starter #13
I'm dubious about there being any wiring faults as you have the ability to switch the brakes on and off with the switch. That tells me that the BCU is receiving the signal and controlling voltage on the output wire.
So how can I check the BCU
 

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I wouldn't necessarily expect codes. I'd be looking at live data to see if the car could see the pedal position. I'm guessing you're just using a chead obd2 scanner?
 

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Discussion Starter #18
I wouldn't necessarily expect codes. I'd be looking at live data to see if the car could see the pedal position. I'm guessing you're just using a chead obd2 scanner?
It’s my dads and he regularly works on cars so I don’t think it was cheap as he isnt that kind of person.
 
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