A switch controls a bank of 2x4 drop in, 277, 3 tube bi-pin fluorescent lights with electronic ballasts. One fixture, in the middle of the run is not working. The ballast was replaced, 2 new tubes are put in and it works, put the third tube in an the light goes out. The fixture is replaced with another from a different location. The third tube is put in and the light goes out. The switch is flipped a couple of times and all of the light come on. The switch is flipped again, the fixture and the one next to it go out. The original fixture is put in another location and works fine. What could it be?
