So you’re finally getting around to replacing the ceiling light fixture when you discover that the wiring insulation has turned to charcoal and cracked off. The usual reason insulation gets ruined is that the bulbs in the fixture exceeded the fixture’s wattage rating. That extra heat literally baked the insulation. Usually the insulation outside of the ceiling box is OK. But you’ll have to repair the damaged insulation inside the box. No, you can’t just wrap the bare wires with electrical tape. That’s not an acceptable long-term fix. Here’s the right way to fix the problem.
Since the wiring in a ceiling fixture is usually 14-gauge, you can fix it with insulation stripped from a 12-gauge wire. Pick up a short length of 12-2 nonmetallic cable and a package of heat shrinkable tubing. Strip insulation off the 12-gauge wires (Photo 1). Next, slide the new insulation onto the old wires (Photo 2). Then secure the new insulation with heat shrinkable tubing (Photo 3). When you’re done, you can connect the new fixture without worrying about the old wires shorting out. Just be sure to follow the wattage maximum of the fixture when you select bulbs.