Quick bit of info first Carlos - if you unplug one of the two bulbs that you were asking about and the other does not go out, they are not on same "circut" because by breaking the circut with one of the lights, it would effectively make the other go out. To my knowledge, everything in a vehicle that is wired with more than one item that does essentially the same thing (front/rear/left/right parking lights, etc) while all share the same common "feed" of electricity, they are wired in parallel. Meaning that that one feed somewhere splits into four (assuming four parking lights) and terminates at four different ground points (which is the entire metal portion of the vehicle chassis) which all lead back to the negative terminal on the battery. So if one goes out, it doesn't affect the others, with the exception of being ever so slightly less load on the battery. I hope this wasn't confusing.
