Solution: Won't light up: Flip it 180 degrees (reverse the polarity). Move the metal pin clips closer so that they can mount the festoon tighter. (You don't have to do that if you think it might break the clips.) Flicker: Try slightly raise the led bulb's metal pin and reinsert (improve connectivity). Because the LED bulbs have lower power consumption, German brand name of cars may need to tap on Load Resistors to remove the error code on dashboard,To remove error message,Please choose T10 canbus bulbs.