I have a 1000W hps ballast I just tried for the first time and it didn't light on 120V or 240V. It did, however, light my metal halide bulb which suggests to me the ignitor is bad. I didn't detect any starting pulses with a 30KVDC volt-meter. The ballast is from Advance and the specified ignitor is LI571. Will any 1000W ignitor work or must it be LI571? I ask because the LI571 is twice the price of a generic ignitor according to a quick google search.

Thanks

I don't think the V-meter would be able to respond only few us HV pulses, you need rather a oscilloscope with HV probe.

Regarding the ignitor interchangeability: The ignitor use the ballast winding as a step-up transformer to generate the required few kV from(usually 200V, but this differ). So the turn's ratio from capacitor (assume CWA) end to ignitor tap and from this tap to hot output should be equal in order to have corresponding ignitors interchangeable. Other option would be the use of superimposed style ignitor. It is a bit bigger (has it's own HV pulse transformer), but it is connected between the ballast and lamp, so would work with any ballast rated for given lamp.