I just installed new headlights and now the turn signal on the left does not work.
I checked the connections and they are ok.
Also the light bulb is OK, checked it with two bulbs and swapped the left and right one.

Is there a fuse or something only for the left turn sigal?
Side and rear signals work fine.

If side and rear work OK, then I'd suggest either a damged wire/bulb holder or earthing problem