D2a Lights Issue

[rangieman]

After a weekend away last week one car i was following stopped and asked why i was flashing him with my (foglights)
Well i didnt or wasnt flashing him but he did say he noticed that it was when he had his brakes on so we assume it is a short some where in the brake light circuit as i was braking the same time.
Now its not the fog lights its the parkers that come on when the brake pedal is depressed dash lights as well.

Checked all earths from Batt to body - ok

Checked all earths behind tail lights - ok

Checked fuse box underdash no sign of melting - ok

I have isolated trailer plug no different .

isolated individual tail lights and both still happens.

isolated trailer brake controler still happens .
Everthing else works as expected.

[kelvo]

I'd try removing the brake light globes one at a time and seeing if it still happens.

It could be the filament in one of the globes has broken and is shorting across internal to the globe, causing a back feed to the parking/side lights.

Rereading your 1st post it sounds like you might have already tried that?

[sierrafery]

Hi, unfortunately this seems a quite complicated issue as IMO when you push the brake the DRL(daylight running lamps) relay(part of interior fusebox) gets active and the only connections between these are through the BCU or IDM, i dont know what "parkers" mean sorry but the DRL relay will activate the dipped beam and the dash illumination if it closes, this could be a IDM missbehaviour too(also part of the fusebox) which gets the inputs from the brake switch but manages the DRLs too

what's easy to check is to not be water ingress/corrosion at the BCU plugs cos the brake switch input and DRL output are both in C0661

if you want to DIY and you have RAVE i'll tell you how to rule this out but i'm affraid you'll have to cut the DRL coil's feed to see if it's IDM or BCU issue...or swap the interior fusebox for a known good one for test

anyway before going so deep into this when you say you've isolated that trailer brake controller do you mean unplugged it?... those controllers used to make all kind of tricks so rule this out first 100%

[rangieman]

Hi, unfortunately this seems a quite complicated issue as IMO when you push the brake the DRL(daylight running lamps) relay(part of interior fusebox) gets active and the only connections between these are through the BCU or IDM, i dont know what "parkers" mean sorry but the DRL relay will activate the dipped beam and the dash illumination if it closes, this could be a IDM missbehaviour too(also part of the fusebox) which gets the inputs from the brake switch but manages the DRLs too

what's easy to check is to not be water ingress/corrosion at the BCU plugs cos the brake switch input and DRL output are both in C0661

if you want to DIY and you have RAVE i'll tell you how to rule this out but i'm affraid you'll have to cut the DRL coil's feed to see if it's IDM or BCU issue...or swap the interior fusebox for a known good one for test

anyway before going so deep into this when you say you've isolated that trailer brake controller do you mean unplugged it?... those controllers used to make all kind of tricks so rule this out first 100%

Yes sorry DRL over here we call them parkers or side lights .
Yes the trailer Brake controller was isolated power + earth any link to the car to no avail
Same prob

[rangieman]

The Brake lights work it is just the parkers and dash lights come on when the brakes are applied, No proplem obviously if the parkers on all is normal.

[sierrafery]

The Brake lights work it is just the parkers and dash lights come on when the brakes are applied, No proplem obviously if the parkers on all is normal.
As long if as you say the parkers = DRLs unfortunately this leads closer to my BCU-IDM theory...let's hope i'm wrong:cool:

[d2dave]

Chris. To rule out the fuse box borrow one from Ken and try it. It is not hard to remove.

[sierrafery]

Be aware, if you swap the interior fusebox disconnect the battery first then after it's plugged in and battery reconnected put ignition on pos. II and leave it so 5 minutes before you do anything else as the digital datalink between the BCU and IDM to be reestablished otherwise the immobiliser might become active.