LED High Beam Flickers When Fog Lights Turn On
I installed a set of Morimoto XB LED Headlight bulbs on a B5.5 VW Passat.
If you have a car that the fog lights shut off when high beams are on, this may happen to you as well, so this is not necessarily a Passat-specific post.
This car comes with a 4 beam headlight system and also has fog lights. There is low beam projectors in the headlights and a high beam reflector. The fog lights are located in the lower bumper grills.
After installing the bulbs and testing, I noticed the high beam bulbs would flicker badly if the fog lights were turned on at all. Parking lights + fog lights = high beam flicker, low beams + fog lights = high beam flicker.
I grabbed a stock bulb and plugged it into one of the high beam sockets and tried again. The flashing went away and everything behaved as it should.
What this told me is that there was not enough resistance in the high beam circuit. I added a single Morimoto HD Load Resistor and that was enough resistance to stop both headlight bulbs from flickering when the fog lights turn on. However the final installation should have a resistor for each bulb.