Used to be some said to screw an incandescent lamp in and if it lights up the ballast was good and if it still won't start correct, working HPS lamp then the ignitor was probably bad.An incandescent will! LOL! I was working on a theatre years ago, noticed the wall pack at one of the outside exits was glowing dim. Opened it up, found maintenance had screwed in a regular light bulb into a medium base HPS fixture! LOL!