Because the Blower resistor gets very hot under normal operation, once the load resistor coils get old (or trash gets on them) the resistance shoots up and will burn the plastic ect around it. They are bolted into the air ducting so the airflow from the blower will cool it. Thus the smoke ect will be distributed through the vents. It's just something I saw happen on countless import and domestic vehicles in the years I have done this for a living. Just a guess, just like everyone else is doing, educated guess w/ clues provided.
Kinda like a game, huh? <img src="/forums/images/graemlins/wink.gif" alt="" />