When you go to euro headlights, the entire headlight unit is replaced. This inludes headlight, foglight, and adjusting systems. Since wiring to the bulb is inside the unit, the difference between H4 and 9004 is irrelevant. The Euro unit will come with all required internal wiring. You will, however, need to convert from a 4-pin to a 6-pin connector to connect main wiring harness to euro unit. Foglight bulb is H3 in both USA and Euro units.