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Brake light not working properly

Tiny
TERRENCEJ
  • MEMBER
  • 2001 MERCEDES BENZ S430
  • V8
  • 2WD
  • AUTOMATIC
  • 208,000 MILES
When I press the brake pedal my driver side brake light comes on then goes off.
Friday, March 22nd, 2019 AT 9:44 AM

3 Replies

Tiny
JOETECHPRO
  • MECHANIC
  • 705 POSTS
Hey TERRENCEJ,

This may sound obvious but have you replaced the bulb?

When the filament heats up it can sometimes cause a break in the connection and as it cools it reconnects.

Please if you haven't done already replace the bulb and retest.

Regards, Joe
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Saturday, March 23rd, 2019 AT 1:16 PM
Tiny
TERRENCEJ
  • MEMBER
  • 2 POSTS
Yes, I have replaced all the bulbs and changed the tail lights with new ones. Also the brake light that is acting up is ran off a circuit board not a bulb.
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Saturday, March 23rd, 2019 AT 1:34 PM
Tiny
JOETECHPRO
  • MECHANIC
  • 705 POSTS
Hey TERRENCEJ,

I have attached the wiring diagram for the rear lights.

If the brake unit portion is an LED and you have already replaced the unit then you will have an issue with either power or ground to the brake light unit or a problem with the SAM module for the rear.

To begin I would get someone to operate the brake light and check for voltage between pin 3 and pin 7 on the light unit connector.

You will need a multimeter for this testing.

Let me know what reading you get when it initially comes on and then what it is with the pedal depressed but no light output.

Hope that helps.

The wiring diagram is attached to this message.

Regards, Joe
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Saturday, March 23rd, 2019 AT 5:47 PM

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