How do I replace this very old dimmer switch with a standard switch

Question

There appear to be a lot of furry wires, 1 black, 1 white wire, and no ground. How do I go about wiring this up to a standard switch? And which remaining wires should I cap together?

Answer 1

Referring to the image below:

1. Carefully tuck these back into the box
2. Carefully tuck these back into the box
3. Connect this to one screw on the new switch
   1. Remove the wire nut
   2. Bend a hook into the the wire coming from the wall^*
   3. Put the hook around a screw on the replacement switch, making sure that the hook goes around the screw clockwise
   4. Tighten the screw, making sure the wire stays under the screw
4. Connect this to the other screw on the new switch. Follow the same procedure as in step 3.

^{Click to embiggen}

Note that grounding is good. It isn't required on switches. The NEC (from 2017, I believe) allows you to add a separate grounding wire to an existing circuit, however doing so is a whole different ball game. Also, it's not required to add it when doing simple fixes like replacing a switch.

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^*Even better would be to spend an extra dollar or so on a "commercial grade" switch that has side clamps. There is no need to bend a hook in the wire - just stick it straight under the clamp and screw it down. Usually, these will allow you to put two wires under the same clamp (one on each side). You can not put 2 wires under a standard screw fitting.

This would allow you to modify these instructions by removing the wire nut at #1 and attach the two wires that go back into the box under one side clamp. The other pig-tail of wire and its nut would go with the old switch into your spares drawer. (TBH, you should get rid of that bit of wire, it's looking rather... ragged.) You would also eliminate step #4 from the above.

Answer 2

You're correct, that is a mess of wires and it's anyone's guess where all those go to at this point. But, to wire a new switch in it needs to go here:

Remove those two wire nuts and place the new switch at those points.

It's not really a part of what you asked but that insulation looks quite old and deteriorating. You may want to consider bringing in a qualified electrician to evaluate what you have going on here.