There is no error if you do it properly. The point is to get this working when default wire is not powering and to get power from default wire when light is on by car.
There is harness someone is selling and link in this post. Despite 50 US$ price I don't like that because low beam is used to detect is light on or off, depending of coding this may raise error in the car (I don't think this is common to have xenon off with HB but I just don't like this). That for I've made my own module (you need to made two of them or twice in one module as I did). Mats price for pair : less than 10 US$.
The idea is to get power from ignition when light is off and to cut this power and use regular power from light module when light is on, that way you will not get any error and car will be able to keep detecting everything as before harness is installed.
If you made two modules each one will have 4 wires :
+ from ignition
+ from light module
wire to AE
If you made one module this will have 6 wires
Anyway, keep in mind that AE in pre LCI headlight is smaller than new ones, so, AE light is not exactly visible as on new cars. This probably can be fixed by opening headlight and scratch AE tube but looks too complicated to me, bake HL already sound scary
I've changed standard bulb with 6W led and this is better than regular bulb but still not like new cars (10 W is bigger and won't fit, you can't close it).
Here is picture without and with flash, let's say this one with flash is what you can see on sunny day like 100 m distance.