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Brake lights

Tiny
GASANDERS
  • MEMBER
  • 2002 MERCEDES BENZ ML320
My brake lights stay on "bright" any time the key is on regardless of brake peddle position. Pumping the peddle and tapping the brake switch will not put them out. Cruise control is inop as a result!

6 cyl All Wheel Drive Automatic 112500 miles
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Friday, March 19th, 2010 AT 6:33 PM

9 Replies

Tiny
CARADIODOC
  • MECHANIC
  • 33,916 POSTS
Check the switch by the brake pedal. It could be out of adjustment or the bracket could be loose or bent. Try pressing the button in by hand to see if the lights go out.

Caradiodoc
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Friday, March 19th, 2010 AT 7:03 PM
Tiny
GASANDERS
  • MEMBER
  • 5 POSTS
Brake peddle switch is tight and properly positioned. It depresses/releases ok and I can hear the gear shift sylinoid clicking as I work the switch with my finger. Brake lights stay on bright at all times with key on regardless of brake switch position.
Cruise control will not engage when driving with brake lights on bright.
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Friday, March 19th, 2010 AT 7:39 PM
Tiny
CARADIODOC
  • MECHANIC
  • 33,916 POSTS
Can you unplug the switch and see what happens?

Caradiodoc
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Friday, March 19th, 2010 AT 9:59 PM
Tiny
GASANDERS
  • MEMBER
  • 5 POSTS
Unplug switch and the Brake lites go out. The switch has 2 plugs, 3 wires each plug. The system also appears to have a relay in the fuse box that puts the lites out when it is removed/unplugged.
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Saturday, March 20th, 2010 AT 6:48 AM
Tiny
CARADIODOC
  • MECHANIC
  • 33,916 POSTS
We can eliminate the relay since it turns off by unplugging the switch. Plug them back in one at a time to see which one causes the lights to turn on again. I would be tempted to pop it apart to see if the contacts are arced together or if a return spring is broken. It any rate, I think you found the problem and it's going to have an inexpensive fix.

Caradiodoc
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Saturday, March 20th, 2010 AT 5:18 PM
Tiny
GASANDERS
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  • 5 POSTS
Thanks; problem solved and lites work normal now. Gary
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Saturday, March 20th, 2010 AT 6:26 PM
Tiny
CARADIODOC
  • MECHANIC
  • 33,916 POSTS
Dandy news. Were you able to fix the switch or did you have to replace it?

Caradiodoc
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Saturday, March 20th, 2010 AT 10:53 PM
Tiny
GASANDERS
  • MEMBER
  • 5 POSTS
Just replaced it! Thanks
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Sunday, March 21st, 2010 AT 6:00 AM
Tiny
2 LINSEY
  • MECHANIC
  • 287 POSTS
Thank you for using 2CarPros. Com. We appreciate your donation and look forward to helping you in the future.
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Monday, March 29th, 2010 AT 2:17 PM

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