Chew on this...

Read this:

My cousin's blog


now you understand this:

Of course, the closest book I had at hand was the manual for my driver's training class:

"Las luces antiniebla delanteras deberán utilizarse simultáneamente con las de posición al menos y las traseras sólo podrán encenderse cuando lo estén también los de carretera, las de cruce o las antiniebla delanteras (15.3.RV)

So chew on that for awhile. See if you can translate it into plain English. (I recommend translating it into plain Spanish, first.)

Note: The Spanish government is no longer allowing U.S. citizens to get their Spanish driver's license without first completely an expensive driver's training course, even if they already have a valid D.L. from the States.