1 Proteus 2 weeks ago Read carefully. I don't need a tutorial on changing ballasts. This is a very specific behavior.We have a dozen or so fairly new 8-ft dual-tube fixtures, with electronic ballasts and the newer lights with molded ends that insert into spring-loaded sockets.I've successfully replaced the ballasts in these, and the lights work properly - so my incompetence would not seem to be a factor.The problem is with one fixture. Important to know: this fixture cannot be switched off, the lights burn all the time. Symptom was that one bulb was out. Replaced with known good new bulb, still nothing. Whether using the functional original bulb and a new bulb, or two new bulbs, here's the significant behavior:One bulb in place, no light. Stick ONE end of the other bulb into its socket, and both bulbs (or only one bulb if one is bad) FLASH once - and that's it. Finish installing both bulbs, nothing lights. It doesn't matter which bulb is plugged in second, nor which end is plugged in - still, when the first end of the second bulb is plugged in, both bulbs light briefly and then go out.Replaced the ballast - and EXACTLY the same behavior.All wire-nut connections have been visually checked and tightened. We've inspected the sockets themselves, and the wires seem snugly inserted. The only clue is that the socket for one end of one bulb appears to have a light surface flash burn. Contacts have been cleaned, however, and the wire feels snug.The ground wire (which connects to a screw into the housing of the fixture) seems tight. I have not loosened it to check that it's making good contact.We know the fixture is getting electricity. We know the bulbs are good. Same behavior with either the original or a new ballast (and I have a hard time accepting that two ballasts would fail with exactly the same behavior).The fact that the bulbs flash ONCE when the second one is connected at one end has to be a clue - but to what?I only ask here because the GDP membership often answers non-guitar questions that the wider internet fails.