Sl55 amg 3rd level brake light (aftermarket rain light wiring) electrical wizards

[Tylerhayles1]

So today i decided install my rain light was recommended to splice into my 3rd high level brake light, as there is only 2 wires sounded easy to me 2 wires from the rain light to 2 wires in the 3rd brake light, dry fitted it all was perfect wedged the brake and everytime i touched the wires together was perfect thought lovely stuff,
then decided to spend 2 hours threading it through the loom so it looked good and not tacky, plugged the cables all in started up car wedged brake and nothing!! 3rd brake light stopped working and rain light would come on quickly then go off for 10seconds then flicker on then off again etc. Its bugging the hell out of me why would it of worked at the start when i briefly connected it then soon as i done it all properly nothing come on, (ps) 3rd brake light works again as normal when i disconnect rain light.

i understand mercedes have canbus etc and sometimes need a resistor, but how did it work at the start then randomly stop,
(Rainlight all works fine)
please help

 

[richard]

What is a "rain light" ???

R

 

[richard]

Also you say: -
Rain light would come on quickly then go off for 10seconds then flicker on then off again etc
And you say: -
Rainlight all works fine

Which is it ?

The bulb failure detection is detecting the high-level brake light is taking too much current now you've added stuff to it that isn't intended and turning it off, and then testing again after 10 seconds and finding the same.

Ps, I found out what a rain light is - are they even allowed on road cars??

 

[Tylerhayles1]

Also you say: -
Rain light would come on quickly then go off for 10seconds then flicker on then off again etc
And you say: -
Rainlight all works fine

Which is it ?

The bulb failure detection is detecting the high-level brake light is taking too much current now you've added stuff to it that isn't intended and turning it off, and then testing again after 10 seconds and finding the same.

Ps, I found out what a rain light is - are they even allowed on road cars??

I mean the rain light is not faulty, i hooked battery pack to it and it works fine,
right yes I understand the way you addressed that, mercedes electrics are a pain, so whats the way to get around it? Add a resistor in?
And im not 100% on the law but its only acting as a lower brake light will come on and off as when i use the brake, most newer AMGs come with factory ones so hmm,
Yeah let me know what you think could work, thanks budd

 

[richard]

Ah, makes sense now

A resistor would have to (a) in series with the new light (b) big enough not to melt (c) placed somewhere where it could cool and not catch fire to anything and (d) it would mean less power for the rain-light which therefore wont be as bright.

If I remember correctly the SL's normal brake lights are not LED and thus you should wire your light there instead, as the car expects those lights to take a load of current and shouldn't notice a LED light added. (standard brake light bulbs are 21w, and your LED thing will take a fraction of that)

Where is the light being put ?

 

[Tylerhayles1]

Ah, makes sense now

A resistor would have to (a) in series with the new light (b) big enough not to melt (c) placed somewhere where it could cool and not catch fire to anything and (d) it would mean less power for the rain-light which therefore wont be as bright.

If I remember correctly the SL's normal brake lights are not LED and thus you should wire your light there instead, as the car expects those lights to take a load of current and shouldn't notice a LED light added. (standard brake light bulbs are 21w, and your LED thing will take a fraction of that)

Where is the light being put ?

Yeah I believe normal brake lights are halogen wasnt to sure what the 3rd level is i potentially thought led,
And yes completely makes sense i get you, i just swerved that option at the start, because the multiplug into back of tail lights have so many cables and that means all sorts of testing and see what cable comes live when brake pedal is pressed etc etc dont think i really know what im doing and dont want to blown circuits etc, apparently the light only draws 0.2A I believe he said.
Lights going on back of car at bottom mounted into diffuser so will look like this