There is probably some variety depending upon the scrap dealer, but the one that we go to will take anything with metal. Items that are not pure metals will end up in general categories and you will get less money for it. Appliances for instance, which might contain a variety of metals, plastics, glass, etc. will end up in a general scrap category and they buy it by the ton. Wiring with sheathing on will be different than wiring without the sheathing, because they have to strip it themselves.
Stripping things down to pure metals will usually get you more money. It depends on the time you want to put into it. You can for instance, break down a motor to pull out the coiled copper wire, but that can be a lot of work. With appliances you can usually do better by stripping out wiring, motors, and aluminum pieces.
Aluminum and copper are the most valuable common metals. I think Copper is over $3 a pound. We also take our tin food cans. They end up as general scrap, so probably don't count for much, but every little bit helps.