Another MSD problem

I came accross the same thing on saturday night, and have
been scratching my head ever since.
I fed the msd off the input side of the ballast and it wouldnt start even though there was power going to the box. But when I plug the ballast back in it starts right up
(the power feed still connected to the input terminal on the ballast)
Is it because the charging circuit runs through the ballast?

Moper, are you saying it doesn't matter if the voltage drops on that particular wire??