What you’re seeing here is two wires that connect to opposite sides of the thermal cutout. One of the wires goes straight back to the wall outlet where the electricity comes from. You’ll notice that the insulation on both wires is red, but appears much blacker in the vicinity of the thermal cutout. One of them is so charred that it broke off its connector, and that’s why there’s no juice getting into the microwave oven.
Replacement parts are available on line. The oven was built in 1990. One thing to consider is, how long is a microwave oven supposed to last?
Another good question is what causes the charring you see in the picture. Usually it’s a high current, too much for the skinny little wire to handle. What caused the current? (I don’t really know) Did the high current happen all at once, or did it happen over and over again for a period of maybe years? (I still don’t know) Is there some other device in the oven that’s failing (probably) that allowed the current to go up like that? (I don’t even know how to check yet) Looks like we’re going to Fry’s again today.