Was board today finished all my christmas shopping so popped into work and set about wiring up my next mod, Ive done this mod to previous cars and always liked it so thought id treat the A4 to the same treatment.
I originally wanted to tap into the power I needed to activate the circuit at source the ccm but after finding out its hidden in the foot well under the carpet and inside a water proof box I decided I would see about tapping in at the dome light and it was here i came up against my first problem due to it being a CAN BUS system it wasn't straight forward, i wanted to pick up the switched 12v power but the 12v power never actually turns fully off for some reason, when there's not 12v going up the wire there's 4.4v and this is enough power to mess things up wiring it through a relay as the relay dosen't shut off unless it goes lower than 4.4v, i then found that the earth is also switched so i ended up using this to activate a relay which then send a fused power source to my DRL circuit..... simple
It all went fairly smoothly the only thing i cant get around is when unlocking the LED bulbs flash a split second before coming on i did try it using standard halogen bulbs and it didn't do it so im guessing its something to do with the way LED's work .
Here's a quick vid of them working:
Remote activation of my fogs rewired as LED DRL's - YouTube
The way I've wired it up means i get no back feed issues when using the interior light of the drls independent of each other, they also switch on once you shut the car off and remove the key from the ignition and stay on till you exit and lock or till the interior light goes out