Ballast Resistor

Thanks for all of the good feedback....one last question....Is there any pattern to them giving out? Mine was just idling at a stop light (on a cool day, for what that's worth). Do they also go out under acceleration....kinda like if you had run out of gas? For some reason I was (wrongly) thinking they only gave out when you were actually starting the car.
Ive heard of guys putting a small spacer between the firewall and resistor for a little air circulation to keep them a bit cooler .Not sure if that helped .