Socket of ceiling or wall fixture defective. Shut off current at fuse box. Take down fixture. Remove coverings on cord splices behind fixture and untwist wires (if they are soldered together, melt solder with a soldering iron or simply cut off soldered portion). Remove socket from fixture and replace with new one. Connect black wire on socket to black lead cable, white wire to white cable, by twisting ends of wires together. Cover the joined ends of the wires with insulated wire nuts, and screw nuts tight. Then wrap friction tape or cellophane electrical tape around base of nuts and wires. Reassemble fixture.
Pull-chain broken below light. Buy a new chain with a split clamp. Open one end of clamp, slip bottom bead of old chain into it and squeeze clamp together.
Pull-chain broken within light. Turn off current. Pull socket apart and note how the chain is threaded into it. Open or pry out the clamp holding the last bead of the chain, thread new chain into socket and place in clamp. Reassemble socket.
Light diffuser broken. If made of glass, apply Duco cement to both broken edges and press together. If made of plastic, use plastic-mending adhesive. In both cases, hold the broken pieces together with adhesive tape while glue dries.