In my office, I have four fluorescent T-8 4'/4 lamp surface mount fixtures. All four are on the same three-way switch. I just replaced 3 of the four fixtures. Two of the new fixtures adjacent to each other (same location opposite sides of the high part of the ceiling) do not work. The other two that work are on opposite sides of the office over both exterior doors. I used a non-contact tester and both non-working lights have a hot wire. Since the other two fixtures work, does this mean I have two separate neutrals? Any ideas on troubleshooting would be greatly appreciated.
Try removing the tubes that are not working and carefully replacing them to ensure good contact. On some fixtures neither tube will light up if one tube in not getting good contact.