Brake lights coming on with tail lights

[awilliams]

Hi

i am running an '05 D3 V8 great car but as with most LRs, a few quirks.

thought I'd ask if anyone has experienced this. During the day, the brake lights are operating as normal. At night when I turn on the head/tail lights, the brake lights come on as well.

I cannot see any obvious shorts so I thought I'd post the question here and see if this is a common thing or a unique little quirk I have to get an auto electrician onto

thanks in advance

Al

[PhilipA]

If they are normal bulbs, probably a bad earth.

It can happen that a filament from the brake light breaks and falls across the taillight filament.

If LEDs you are on your own.
Regards Philip A

[awilliams]

Cheers Philip... just curious, would that cause all of the break lights to come on? BTW they are normal lamps, not LED so I'll check it out

thanks
Al

[awilliams]

Sadly this has not been the cause... just checked out the bulbs and replaced one suspect... i actually decided to unplug each one individually and retry. same issue. hhhmmmm :confused::confused:

[snowbound]

Will be a bad earth for sure, unless you been mucking with something. Rust is your enemy! :evil:

[Marmoset]

Mine does that when I have my bike rack trailer board hooked up. Only happens when the lights are turned on - I suspect a wiring fault on the earth side but haven't had the time to investigate it further. If you have trailer electrics on your it might be worth checking them over visually for any chafing etc.

Mine threw up a transmission error when this was happening and it can make the car think that you want engine braking when you are accelerating in "D" (I think the gearbox ECU has a brake switch input) so the revs climb sky high and the box doesn't shift up. Shifting works fine in command shift though if this ever happens to you.

[Blknight.aus]

have seen this caused by a short in the trailer plug...

[rocmic]

Just a quick question (and probably completely off track), it's not the fog light rather than the break light coming on, could be a faulty headlight switch if that is the case?

[awilliams]

Hi guys,

I havent used the trailer connectors for a while but interestingly, I am getting an intermitent Transmission fault which Marmoset mentioned. Is there a possible connection with the brake switch unit?

thanks again

[awilliams]

sorry , meant to mention that it is not the fog lights... definitely the brake lights including the high mount stop light at the top of the tailgate.

[Marmoset]

For what they cost, I'd get a new brake switch and try that - I think I found one for around $20 on ebay. Didn't buy it as I'd figured out the bike rack thing 5 minutes later....

[GregD2]

Does the vehicle have electric trailer brake controller fitted ? If so I know that the trailer plug on a d3 has 2 park light circuits in it and one needs to be removed if electric brakes fitted if not then it can back feed and cause the brake lights to come on when the park lights are on. Hope his helps.

[awilliams]

Thanks guys, I am unsure if its fitted with an electric trailer brake controller. I will try the brake switch first and dig deeper if its still an issue.
:confused: