I am sure I know the answer but I will put it out there anyway on the off chance someone knows. Does anyone know of a car with LED headlights that has had driving lights fitted and they work. We are attempting to fit driving lights to my Tiguan and are having trouble getting a suitable signal voltage to the relay from the high beam circuit. My son works as a day job doing diagnosis and repair on new cars at a very high level though not on VW unfortunately and he can't find a way to access the signal that will work. If we pick up the signal from the wiring loom going into the light the lights stay on and won't return to low beam. He thinks there is a controller in the light itself and we are interfering with that, could be of course and maybe this won't work at all. A single 12v rail seems to be supplying current to the headlight and the PCM or controller in the headlight decides what function in the light needs to see that 12v rail and needs power. The headlight switch has a 0.2v signal wire that happens when the switch goes to high beam which would make the above scenario work.
I am guessing in my naive way that if we had an external controller/relay that could use the 0.2v reference signal from the switch then the problem goes away but that part is beyond our knowledge, anyone got any ideas?