KW T2000 Sleeper/Dome Light

Driving a 2000 T2000. The fluorescent light in the middle of the cab quit working. The are just 15 watt, 18" regular fluorescent bulbs. I replaced them yet the light still isn't coming on.

I pulled it out today thinking the ballast(?) was bad. But its not a typical compared to the ones in my garage. This is like a circuit board.

I took a test light and I had power at the plug. I also had power at different parts on the ballast/board. But at the end where the lights slide in I couldn't get my test light to come on.

Could the circuit board/ballast be bad? Or could the problem be else where? I'm not that versed in electrical or fluorescent lamps so I'm not sure if I'm looking at the right place.