trailer brake lights not working - OBVIOUS ERROR
Thread Starter
Senior Member
Joined: Oct 2015
Posts: 397
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From: Queensalnd Australia
2006 ML320 CDI (2 of) and 2008 GL320
trailer brake lights not working - OBVIOUS ERROR
I just had the problem with daughter driving a horse in a float back here and the brake controller was not working - I tried to diagnose her over the phone (she was 200km away) but as far as I could work out the controller wasn't getting the message that the car brakes were on. She ended up driving the 200km with no brakes to trailer
When the car gets here I notice that the brake lights on trailer were not very bright
The multimeter shower only .8v to brake lights -
I then noticed we had the message on dash that the left brake light out and back up lights on (but hey its a W164 that's not unusual)
It was then obvious that the brake controller wasn't getting signal (enough) from brake circuit as it was in backup light mode.
Sorted out the globe holder contacts and all good
I just thought I would mention this as it didn't occur to me initially that if the error message is up that the normal brakelight circuit is not getting full power..
I should also mention that I have found that the globe holders off BMW E36 (I have wrecked a few of these) work better in the ML than the merc ones, they are a bit longer so it is easier to get the fingers in. I have swapped them the other ML and its way better
When the car gets here I notice that the brake lights on trailer were not very bright
The multimeter shower only .8v to brake lights -
I then noticed we had the message on dash that the left brake light out and back up lights on (but hey its a W164 that's not unusual)
It was then obvious that the brake controller wasn't getting signal (enough) from brake circuit as it was in backup light mode.
Sorted out the globe holder contacts and all good
I just thought I would mention this as it didn't occur to me initially that if the error message is up that the normal brakelight circuit is not getting full power..
I should also mention that I have found that the globe holders off BMW E36 (I have wrecked a few of these) work better in the ML than the merc ones, they are a bit longer so it is easier to get the fingers in. I have swapped them the other ML and its way better
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From: Bronx, N.Y.
2002 ML 320 & 2006 ML500
Swap the left & right bulb holders w/bulbs. If the problem switches to the other side, then it is the bulb or the holder.
If the problem remains on that side, then you must order two repair kits (top of page #3), from the dealer, and install repair harnesses. This of course depends on the fact that you do not have a scanner to read codes.
If the problem remains on that side, then you must order two repair kits (top of page #3), from the dealer, and install repair harnesses. This of course depends on the fact that you do not have a scanner to read codes.
Thread Starter
Senior Member
Joined: Oct 2015
Posts: 397
Likes: 23
From: Queensalnd Australia
2006 ML320 CDI (2 of) and 2008 GL320
Thanks for the link, I have one of the Autel scanners but have not done so as yet because it has always been in the holders for me
In my case it is definitely in the globe holder - scrape a bit of oxidisation off the terminals where they make contact with the light and bend them up a bit (to make better contact) and they seem to not cause problems for ages.
The other ML did the same thing and I swapped most of the holders with BMW E36 ones (I mainly did it because they are longer and easier to get at in the ML but perhaps they make better contact as the other car has no caused problems since I did it)
I mainly started this thread because I had not previously made the connection with the stop lamps going into "backup" mode and not putting power to the brake lamp circuit on a trailer
In my case it is definitely in the globe holder - scrape a bit of oxidisation off the terminals where they make contact with the light and bend them up a bit (to make better contact) and they seem to not cause problems for ages.
The other ML did the same thing and I swapped most of the holders with BMW E36 ones (I mainly did it because they are longer and easier to get at in the ML but perhaps they make better contact as the other car has no caused problems since I did it)
I mainly started this thread because I had not previously made the connection with the stop lamps going into "backup" mode and not putting power to the brake lamp circuit on a trailer
MBWorld Fanatic!
Joined: Oct 2011
Posts: 7,107
Likes: 765
From: Bronx, N.Y.
2002 ML 320 & 2006 ML500
Thanks for the link, I have one of the Autel scanners but have not done so as yet because it has always been in the holders for me
In my case it is definitely in the globe holder - scrape a bit of oxidisation off the terminals where they make contact with the light and bend them up a bit (to make better contact) and they seem to not cause problems for ages.
The other ML did the same thing and I swapped most of the holders with BMW E36 ones (I mainly did it because they are longer and easier to get at in the ML but perhaps they make better contact as the other car has no caused problems since I did it)
I mainly started this thread because I had not previously made the connection with the stop lamps going into "backup" mode and not putting power to the brake lamp circuit on a trailer
In my case it is definitely in the globe holder - scrape a bit of oxidisation off the terminals where they make contact with the light and bend them up a bit (to make better contact) and they seem to not cause problems for ages.
The other ML did the same thing and I swapped most of the holders with BMW E36 ones (I mainly did it because they are longer and easier to get at in the ML but perhaps they make better contact as the other car has no caused problems since I did it)
I mainly started this thread because I had not previously made the connection with the stop lamps going into "backup" mode and not putting power to the brake lamp circuit on a trailer
Thread Starter
Senior Member
Joined: Oct 2015
Posts: 397
Likes: 23
From: Queensalnd Australia
2006 ML320 CDI (2 of) and 2008 GL320
Stop lamp warning on display (backup bulbs in use) will stop trailer brakes working (as trailer brake controller works off brake lamps - which the computer in the car doesn't send power to when it thinks a bulb is out
Sorry if I am being unclear
Do the US cars have same messages when the stop lamp bulbs get bad connections.
AND I have found BMW E36 (model of 3 series BMW) globe holders work better in the W164 than the MB ones.
Sorry if I am being unclear
Do the US cars have same messages when the stop lamp bulbs get bad connections.
AND I have found BMW E36 (model of 3 series BMW) globe holders work better in the W164 than the MB ones.
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Thread Starter
Senior Member
Joined: Oct 2015
Posts: 397
Likes: 23
From: Queensalnd Australia
2006 ML320 CDI (2 of) and 2008 GL320
I see the confusion
I am referring to the plastic (white for indicator, black for tail/brake lights etc) that holds the globe and fits into the tail light assembly, they too are a bayonet type fit
These are the items I have found to be "better" in the E36 BMW - they just clip straight into the ML tail light assembly (red lite only - not indicators - have not tried reverse)
I have always found that the points of contact for the "globe holder" to the tail light assembly are the issue (at least in the 2 of 2006 ML's I have here)
You can even see a small arc there when the light is activated the contact is so poor.
The E36 ones have a bigger contact, and also the plastic part is longer so you can get a better hold with the fingers
On the ML indicators I do often have to bend the metal terminal to try and get them to make better contact - unfortunately the E36 ones do not work in the ML indicators - I normally squeeze the sides of the contact with long nose pliers to put more of a "dish" in it
I never get any water around there (in either car) or in the boot etc so cannot see a failure in the seals
I am referring to the plastic (white for indicator, black for tail/brake lights etc) that holds the globe and fits into the tail light assembly, they too are a bayonet type fit
These are the items I have found to be "better" in the E36 BMW - they just clip straight into the ML tail light assembly (red lite only - not indicators - have not tried reverse)
I have always found that the points of contact for the "globe holder" to the tail light assembly are the issue (at least in the 2 of 2006 ML's I have here)
You can even see a small arc there when the light is activated the contact is so poor.
The E36 ones have a bigger contact, and also the plastic part is longer so you can get a better hold with the fingers
On the ML indicators I do often have to bend the metal terminal to try and get them to make better contact - unfortunately the E36 ones do not work in the ML indicators - I normally squeeze the sides of the contact with long nose pliers to put more of a "dish" in it
I never get any water around there (in either car) or in the boot etc so cannot see a failure in the seals
MBWorld Fanatic!
Joined: Oct 2011
Posts: 7,107
Likes: 765
From: Bronx, N.Y.
2002 ML 320 & 2006 ML500
Thread Starter
Senior Member
Joined: Oct 2015
Posts: 397
Likes: 23
From: Queensalnd Australia
2006 ML320 CDI (2 of) and 2008 GL320
Is there any way of knowing if the tail light seals have been changed? Obviously I would have hate to change them if they have already been done
MBWorld Fanatic!
Joined: Oct 2011
Posts: 7,107
Likes: 765
From: Bronx, N.Y.
2002 ML 320 & 2006 ML500
Yes, remove the right tail lamp and if the seal is attached to the lamp, they must be replaced because the seal must be attached to the body opening.
Only pull out the lamp enough to see where the seal is stuck to, then push it back in and order the seals.
Last edited by Maj. Dundee; Apr 26, 2019 at 06:31 AM.
