Ballast Resistor

I remember guys installing one right under the factory one ,they only had to switch wires in seconds .I installed Pertronix in my dart with the original distributor and by passed the 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.