With the switches off...take the black lead of your multimeter when on a high enough acv scale so you don't go into overload, place it on a known good ground...the round pin of a receptacle should be a good place. Then, touch the red lead of your multimeter to each wires to see if any have power on them. Make notes, and maybe put some tape on them to mark so you don't forget, or take a picture and put notes on it. Then, turn whatever switch(s) on individually, and see if there's any change in what lines you may have power on.
This may not be definitive, as you can get some weird indications in a high impedance circuit, but may be enough to help figure out what's what.
Is your stove gas, or electric? On a gas stove, they typically have 120vac for their lamps and other electronics, but on an electric stove, they use 240vac, but usually have a neutral to let 120vac stuff run. That isn't universally true especially with some imports, but mostly on stuff sold in the USA. Given the gauge of wire, if it was doing anything to a stove, it would likely be a gas one. Can't think of a good reason why it might affect your microwave, though!