Anorien,
I've done exactly what you have described, it took me a while to get working, but here goes :
B6 A4 TDI Avant, 2002
aftermarket HID by KDG
low beam works a treat
high beam cuts out as the bulb warms up and the bulb blown alarm sounds.
Bulb alarm sounds when ignition II is activated.
I tried wiring in a 22R, 25W resistor in parallel with the input to the ballast to simulate a normal halogen bulb better, but it still cuts out. Bulb alarm sounds when ignition II is activated.
Sames as above, but with two 22R resistors in parallel, made no difference. Bulb alarm sounds when ignition II is activated.
In both cases the power is cut off to the ballast. However, if there is no ballast connected at all, the Bulb alarm still sounds when ignition II is activated, but there is +12v !
So I used the original high beam bulb feed to activate a relay which in turn powered the ballast from the battery.
This worked a treat for me. Except the bulb alarm sounds when ignition II is activated and when high beam is switched on.
I wired in the 22R, 25W resistor in parallel with the input to the ballast to simulate a normal halogen bulb better, but it still cuts out. Bulb alarm sounds when ignition II is activated.
Sames as above, but with two 22R resistors in parallel everything was ok. I am speculating a 15R 25W would do ok. I've yet to order a pair, as the lights are working now, but the bulb alarrm is annoying, so I'll do it soon.
This has been my experience, of course ymmv.
Also have you found any issues with radio reception ?