Does it have a light sensor maybe that is somehow being triggered, or not? At such a low wattage, the cord gauge shouldn't really matter, within reason, as long as the connections are tight. Even a very thin 18gauge cord would be enough, though I doubt I'd personally use something that thin.

I've never used a low wattage HPS but my 400W doesn't turn on/off/on like that - it starts low and builds up to full brightness, but never appears to go off once the power is on.

Lastly make sure the bulb is firmly seated in the socket, but don't tighten it too tight - you should be able to remove it easily.

Sounds like a sensor problem...when you start up a HPS or MH they start up dim and discolored and they slowly get brighter. I am thinking that when it gets to a certain brightness a reflection triggers the sensor to shut the light off. As soon as it turns off it turn right back on...but the bulbs cannot restrike when hot because the gases only ignite at a certain temperature. Once it cools off enough it restarts and gets to brightness and so on...

Put something dark over the sensor and see if that remedys the problem...

~J~

No, It the light bulb. Need to replace with a new one. Bad lamp will cause this problem.

^Yes. Replace it with a grow light. I purchased a 150w hps for $110 and I grow one large cherry tomatoes under it.

Make sure the bulb is the right type and wattage for your ballast.