Metal Halide question

I have a 400 watt ballast and fixture, with a 250 bulb. It has a magnetic ballast, and was direct wired before. In it's previous location this combo worked just fine, but when I brought it home I spliced the wires from the ballast onto the female end of an extension cord. This method of plug-and-play worked great for a 150 watt metal halide, can someone tell me why my 250 watt isn't firing up? The ballast sounds like it's hot, but the bulb isn't lighting up. I've tried this unsuccessfully with two other ballast, but successfully with two as well. The two that worked are 150 watt, the two that didn't were 250 watt. It runs on a standard household 15 amp circuit and should not be taxing the capacitator. Any thoughts?

Well the problem is your are using 250W bulb in a 400W ballast. That doesn't sound right, and maybe dangerous? Use the corresponding light for the ballast, 400w ballast = 400w light, 1000w ballast = 1000w light, etc..be safe!

There's no chance of fire, the wattage of the bulb does not exceed capacity of the ballast. Also, this exact setup worked in it's previous location. I'll try the 400 watt bulb, but still wondering why it worked in it's old location, but not the new one. I assumed that maybe it was an incorrect voltage assignment.