R/R Brake Light Out - But Bulb's Okay
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Joined: May 2003
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From: Washington DC / No. Virginia; and Cape Cod, MA
'71 280SE
R/R Brake Light Out - But Bulb's Okay
I've searched the postings, but haven't found this discussion.
Right rear brake light went out, got the message on the dash. No problem - put in a new bulb. Original bulb looked pretty good though and, sure enough, new bulb did not solve problem.
Swapped bulb mounts; right rear brake light still out. Left works fine, so I know the bulb and housing are fine.
Are there known trouble areas with either the brake light assembly or wiring? Next steps for troubleshooting?
Thanks,
Ed
Right rear brake light went out, got the message on the dash. No problem - put in a new bulb. Original bulb looked pretty good though and, sure enough, new bulb did not solve problem.
Swapped bulb mounts; right rear brake light still out. Left works fine, so I know the bulb and housing are fine.
Are there known trouble areas with either the brake light assembly or wiring? Next steps for troubleshooting?
Thanks,
Ed
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Joined: Jan 2004
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From: Seattle WA
99 E320
turn key to position 1.
apply volt meter to the right brake housing 'traces' and see if you get voltage.
do same when brake pedal is depressed. if yes to both, then your bulb holder
is suspect and probably requires a little tweaking of the contacts on the holder
apply volt meter to the right brake housing 'traces' and see if you get voltage.
do same when brake pedal is depressed. if yes to both, then your bulb holder
is suspect and probably requires a little tweaking of the contacts on the holder
Last edited by raymond g-; Nov 2, 2012 at 09:53 PM.
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I had this problem about a year ago. I found that there was a dimple created in the metal of the light housing where the bulb holder rests. I used a piece of sandpaper on the light housing to remove the dimple and I have not had a problem since.
Thread Starter
Member
Joined: May 2003
Posts: 84
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From: Washington DC / No. Virginia; and Cape Cod, MA
'71 280SE
No Luck
I cleaned all the contact surfaces. Keep in mind both holders work on the left, neither on the right.
Raymond - With the system powered up and bulb holder out, I get no voltage across the housing. Press the brake pedal, meter reads 13V.
I'm stumped.
Raymond - With the system powered up and bulb holder out, I get no voltage across the housing. Press the brake pedal, meter reads 13V.
I'm stumped.
MBWorld Fanatic!
Joined: Jan 2004
Posts: 5,939
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From: Seattle WA
99 E320
switch (on the dash) turned at least 1 click CCW?
the brake pedal press resulted in deflection so that is good, yes? it means
voltage is getting to the rear housing.
but now I begin to suspect your description.
Right rear brake light went out, got the message on the dash. No problem - put in a new bulb. Original bulb looked pretty good though and, sure enough, new bulb did not solve problem.
depressed)?
you really need to be precise and be our eyeballs on this:
- amber=turn signal,
- white=reverse light,
- red=running light,
- red=brake light when pedal depressed
Senior Member
Joined: Jan 2010
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1997 E300D
Look closely at the contacts on the tail light assembly. In my case the bad contact between the bulb holder and the tail light assembly had overheated and melted the plastic under the contact, allowing the contact on the assembly to sink into the tail light enough to give poor contact with the holder. When the corresponding contact on the holder was tweaked or bent out, It worked for awhile. I eventually raised the contact on the assembly by prying it up and putting a shaving of wood under it, to bring it up to the same level as the other two contacts on that bulb hole.
Another option would be to put a blob of solder on that contact on the bulb holder so it would reach the recessed contact. I used that trick on the melted contact on my third brake light.
The three contacts on the assembly are ground, tail light, and brake light. If your tail lights are off and brake not engaged, you should have no voltage on any of these contacts.
Another option would be to put a blob of solder on that contact on the bulb holder so it would reach the recessed contact. I used that trick on the melted contact on my third brake light.
The three contacts on the assembly are ground, tail light, and brake light. If your tail lights are off and brake not engaged, you should have no voltage on any of these contacts.
Last edited by nelbur; Nov 4, 2012 at 11:26 PM.
Thread Starter
Member
Joined: May 2003
Posts: 84
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From: Washington DC / No. Virginia; and Cape Cod, MA
'71 280SE
Thanks, Gents.
Let's recap:
- right BRAKE lamp is out (not tail lamp)
- with bulb mount removed, I measure 13V across the socket with the ignition on and foot on the brake pedal; zero with my foot off the pedal
- light control switch (headlights, parking & tail lights) is in the OFF position
- all contact surfaces have been inspected and cleaned
- EACH bulb and mount works on the driver's side
- neither works on the right
(- same results if bulbs are swapped between mounts)
I'm not terribly handy, but it seems to me that I have voltage when I'm supposed to at the housing and two confirmed working bulb/mount assemblies, just not when I put them together.
Your thoughts?
Thanks,
Ed
Let's recap:
- right BRAKE lamp is out (not tail lamp)
- with bulb mount removed, I measure 13V across the socket with the ignition on and foot on the brake pedal; zero with my foot off the pedal
- light control switch (headlights, parking & tail lights) is in the OFF position
- all contact surfaces have been inspected and cleaned
- EACH bulb and mount works on the driver's side
- neither works on the right
(- same results if bulbs are swapped between mounts)
I'm not terribly handy, but it seems to me that I have voltage when I'm supposed to at the housing and two confirmed working bulb/mount assemblies, just not when I put them together.
Your thoughts?
Thanks,
Ed
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Senior Member
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1997 E300D
The bulb used for the brake light is also a tail light, with two filaments and three contacts. You appear to have a problem where the bulb holder contact fails to make electrical contact with the brake light contact on the tail light assembly. You will have to look closely to figure out why.
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MBWorld Fanatic!
Joined: Jan 2004
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From: Seattle WA
99 E320
The bulb used for the brake light is also a tail light, with two filaments and three contacts. You appear to have a problem where the bulb holder contact fails to make electrical contact with the brake light contact on the tail light assembly. You will have to look closely to figure out why.
butterfly tabs on the bulb holder...or the metal contacts on the back of the
taillight assembly. you're home free
