I have an old house (1905), there is still a reasonable amount of live knob and tube servicing the basement and first floor lighting circuits. I am slowing rewiring as I remodel the house room by room. I have a switch to the basement that is on the knob and tube circuit, the switch is flakey and needs replacing. I want to cut open the wall, and put a junction box in so that I can put in a modern switch. I was thinking of taking out the knob and tube upto the switch and running romex down the back of the wall. I would rather not rewire the entire k&t circuit at this time, so I am looking for advise on how best to make the connection between the section of romex running to the switch and the existing k&t circuit in the basement. Is there some sort or special connector I should use for this, or do I treat the K&T like a pigtail and simply join it to the romex with a cable-twist?

Any advise would be appreciated.
Thanks,
-Brett.

First Brett let me say “Congratulations and Happy New Year” you’re the first subscriber to place a posting on the Ultimate Bulletin Board in this new Millennium.
Okay getting to back to your situation, all new splices made today are to be constructed to meet current code regulations. So make sure this splice is made in an approved metal or non-metallic box and accessible, meaning don’t buried the splice box in the wall you just cut open.
If you use a metal box there are porcelain and plastic bushings available that you can use, if you use a non-metallic box just be sure the integrity of the insulation on the knob and tubing is in good shape and you won’t have to use a bushing.
Enter in your knob and tubing from two separate ‘knock-outs’ ( one wire/one hole/one bushing ) and then enter in your romex on the other end also using an approved romex connector and make your splice accordingly.
Be sure to put a cover on the box when you’re done. I know this may seem a bit ridiculous seeing you have exposed insulated conductors entering the junction box, but to finish off this project properly you need that cover.
Well there you have one way of doing this project, good luck and let us know how it turns out.