I'm in the process of replacing a light fixture with a ceiling fan. I replaced the old mount with a pan ceiling support box. The wiring is old (1920s) and inside armored cable coming through the stud. I brought the cable into the box using a duplex clamp and am left with wiring that is too short.
What is the best and safest way to extend this wiring without having to go into the attic replace it completely? I assume I will need to purchase new wire, splice and attach with a wire nut. But which wiring do I buy? And does it matter which wire nut I use?