I have had some troubles with my 1000w HPS Ballast. It is a older model. I tested it at the light cord socket and am getting around 380 volts. I unplugged the unit and fogged the room two hrs later it will not restart.
Im not sure, but it could have been spiking trying to fire a bulb, it takes a while after the ballast fires the bulb for it to settle in to a sweet spot and run efficiently.
Sounds like the main capacitor in it is fucked. Either get a new ballast or try find a replacement capacitor on the net. There are a few sites selling them. If you know basic electronics then its a sinch to replace.
Added: in saying that, high ampere capacitors do have a tendency to hurt too if you connect with them when theyre charged up. I believe theyre like 16amp capacitors, ouch.
The ballast does sit and humm continous but the light never powers up. I tried two different bulbs with no luck. I know power is at the plug set since i tested both ends of the cord with a meter. I have no idea I just assume something inside the ballast is out. I was thinking maybe a ignitor?