Help with shared neutral and wiring for disposal

jtorral said:

Hi

My house apparently is wired in an old fashioned way with what I believe is called a shared neutral ??? Dont really know. But my breakers are special they turn two circuits off at a time and instead of a black wire only, one breaker has a black and the other a red.

So, I need to hookup a garbage disposal unit and when I remove the cover plate to put in an outlet. However, the only wire on its own ready to tie into an outlet is a black one. There are some other wires tied together and I am sure one of those is supposed to be the neutral.
The black wire on its own does indeed get controlled by the switch on the wall. However I need help identifying which one to use as a neutral for the outlet.

Please see the attached image of my drawing so you can see what I have and maybe you can answer the question. Where you see a dot connecting the two wires indicates a wire nut.

I thank you in advance for your time looking at this.

Diagram and switch wiring attached

Click to expand...