Side light / DRL turns off on one side when brake light illuminated

[davebond101]

Hi All,

First time posting, long time lurker. I do not believe this has been covered before but please point me in the right direction if it has.

I have a VW T6 that I have upgraded the front headlights to LED. These are the THQ ones, and very good they are too. The local mechanic installed them and did the mapping required to stop the bulb failure on the dash illuminating. This step I am not sure exactly what he did.

We noticed that the front passenger side light / DRL (they are combined on the THQ head light) was flickering from seeing its reflection. We spoke with THQ and they sent another light unit and I have just fitted it. We are now noticing that once the brake is depressed rear brake lights iliminate the front passenger side light / DLR goes out (it does not matter if the strip is running as a DRL or as a side light). It is restored once the brake is released. The lower strip on the THQ lights is the side lights, DLR and indicator all in one LED strip.

The unit by design turns these off when indicating as they share the same LED strip. But this always recovers after indication is turned off, but the passenger side light / DRL always goes out once the brake is depressed, and recovers once released.

Any thoughts what is going on here? Feels very wierd!

 

[Dundee_Kev]

Is the problem only since the headlights were fitted? Or has other electrical work been carried out? What happens if you were to pop the original lamp back on?

 

[davebond101]

I believe this is new behavior, I will check tomorrow with the originals as I have just popped out to see if the wiring loom will reach up to one balanced on top and sadly its about 3" too short to test that way. Needs dismantling to do it.
I did wonder if there was any possibility of coding being the issue. I can see many ways DRL can be turned off, and I wondered if this was even possible? Though not sure why this functionality would be there DRL off when breaking ....

 

[Dundee_Kev]

There is coding to turn of DRL when parking brake is applied.

Would be interesting to if there are any fault codes logged.

 

[davebond101]

It's the, it only happens on one side that is getting me. Thought about fuses if there was one per side and it was high resistance. Or if there was a relay.

I don't believe there is a relay, and there looks not to be a fuse for each side only a common headlight fuse. Correct me if I am wrong. Tbh the only fuse box diagrams are on this forum and are very good. But these DRL lights are not from the fuse listed as I believe they are piggy backed from somewhere else.. enabling the Drl requires coding and these are plug and play assuming you don't have LED h7 option....

 

[davebond101]

With an odb reader there are no errors recorded. Any thoughts where to get a headlight loom extender from? With the local weather and outside temperatures a loom extender makes it a very simple job, to put the ond unit on top and test to see if it's repeated with the original lights. Where as taking it apart in the rain and cold fills me with less joy.

 

[davebond101]

Adding a bit more slightly as an inner monologue. But others may have good input on these thoughts. I believe the below is a male and female headlight plug.

Headlight Front Lamp Connector 10 Pin 1J0973735 1J0973835 for AUDI VW

Prewired with approx 15cm Cable OE Part Numbers : 1J0973735 & 1J0973835 10 Pin Connector For Headlights

auto-connectors.co.uk

I plan to make up an extension to the loom and try out as suggested above the original light. Benefit of this is I am not out on the drive for an hour in the rain putting the old light back in as the existing loom does not reach otherwise. I can test with it on the top. Feels more time efficient.

Either shows oddity with headlight unit or other oddness yes to be determined.

Looks to be the right plug pair... Does the hive knowledge of the forum agree?

 

[davebond101]

With my new loom extender I have tried out the old light. The fault is not seen.
While you may think the fault is then with the headlight, I have replaced the entire unit. So there are no common parts.

A thought I did have is the current pull difference between an LED and the bulb of the original. Does anyone have a pinout of the 10 pin plug so that I might add a resistor in series to make the LED's "look the same" as the bulb of the original.

Any thoughts welcome of what else might be wrong. Where one side DRL / side lights go out when the brake is depressed.

 

[roadtripper]

Only thought I have is that on some rear lights the sidelight/drl area can reduce so the visual separation between the brake and sidelight is obviously.

Not sure how that would impact the front and only on one side.

Have you had someone watch the rear lights and see if they are doing something on braking?

 

[Dundee_Kev]

Try disconnecting the tail lights and see what happens. If it solves the issue then plug one back in at a time to determine which side causes the fault.

Unless I've misread your first post, it appears that the second light has produced a different fault to the first. So are there a batch of faulty lights??

 

[davebond101]

The original VW non led lights the fault is not seen. Thq lights the fault is seen even on a second replacement unit.

Fault seen on thq is when brake light illuminated, Drl lights or parking lights are not illuminated on one side. Recovers after brake released. Drl and parking lights share a common led strip.

Now I don't think the thq ones are faulty as it's unlikely that the replacement also shows exactly the same issue. It's not seen on the originals so my thoughts are it's the difference in load like maybe the LEDs pull 2w and bulb pulls 5w maybe. the Drl and sidelight share an led strip. So I think it may be related to how the van sees this.

Please can you elaborate on why removing a rear light? If the fault is not seen on the original, then this is not an intrinsic fault with the van.

If load related I may just need to add a resistor to make the led look like a bulb.

Does anyone have the pin out for the connector? Yes a batch of faulty lights are possible but this is not something thq feel is likely. Out of thousands shipped they say only 6 were faulty.

 

[roadtripper]

One reason is that a brake signal turning a DRL off is a common thing in rear lights. It's also where a wiring fault between the two circuits is likely.

If your headlights are showing an interaction with brake lights, especially across 2 different units, there is a strong chance the fault is in the rear light.

 

[roadtripper]

One reason you may not see this in the original is that LEDs can be sensitive to faults that conventional lamps are not - for instance a conventional lamp will light with current flowing either way, an LED will not.

If you have an existing bad earth somewhere it might be able to earth through the conventional fitting but not the LED

 

[davebond101]

Thanks for that. Makes more sense now explained. Will have a look

 

[davebond101]

Just cleaning the brake light contact on that side has reduced this to a single flicker. The rear light cluster appears to have gotten wet.

Thanks all for your thoughts and ideas. Not completely resolved but massive improvement to a single fraction of a second flicker.

 

[roadtripper]

Looks like something partially earthing through another circuit as it's gone high resistance

Give it a good clean with some contact cleaner, try not to scrape as it will make it more vulnerable to future corrosion.