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Roger, BMW Master Tech
Category: BMW
Satisfied Customers: 5895
Experience:  10 yrs. experience as BMW Master Technician, shop foreman and dealer.
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Why would both brake lights go out at same time on ...

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Why would both brake lights go out at same time on 1999 BMW M Roadster? All fuses have been checked and none were blown. IS THERE A RELAY AFFECTED?

Hello. If you lost brake lights on both sides it could be that your brake light switch is faulty. This is a switch at the brake pedal under the pedal that sends the signal to activate the rear brake lights. I would check the basics first and try a new bulb to make sure it is not in the bulb. If they still do not light then the next step would be the brake light switch. This switch is pretty difficult to replace and I recommend the dealer to install it. If should be no more than a 1 hour labor charge and should save you a lot of headache. Thank you. I hope this is helpful to you.

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Customer: replied 9 years ago.
I'll put a multimeter on it before and after the switch to find current if you recomend.
You could try to see if you have voltage. I would check at the connector itself when the brakes are pressed to see if the voltage is at the connector. It is always good to keep things simple at first when diagnosing something like this. Since both lights are out you need to think of the common denominator between the two which would be the brake light switch failure. I have replaced many of these for this problem. The problem could be deeper like wiring damage or a bad lamp module but this would be the best first step as it is the likely cause. I hope this fixes the problem for you.
Customer: replied 9 years ago.
No problem. I hope the brake light switch corrects this for you. Just a thought though so you know. I am thinking the brake light switch would be an input to the lamp module to acitvate the rear lights. You might have good voltage at the connecter even though the switch is bad as the lamp module would switch the ground on to activate the lights. I would have to look up the wiring diagram to know for sure but just thought you should know. Thank you.