ballaster question

I am having some issues with my 70 dart /6. I bought the car as a winter ride in November and it is doing it's job for my short commute except that I have gone through 2 ballasters. 4 months ago replaced the one that came with the car and then today had to use the old spare that I carry around after the new one failed. wiring? the connections seem tight. this car is rough body wise and the ballaster probably has some exposure to the weather.