Originally Posted by RadioTek

You might also want to check the ballast resistors and their connections, too.

This sounds like an intermittent electrical problem, but that's only a guess over the 'net. Intermittents are hard to find, from my experience. You need to look at all the connectors, components, wires, and switches to isolate your trouble. Sometimes going through everything and tightening the connections will let you find the problem, you could find something that's half-way hanging on, a loose connection, a poor or corroded connector, a bare wire (the abovementioned green wire is notorious), or the proverbial dead wombat in the works. Patience is required.

Happy Hunting,
Scott