Any 14-16 gauge wire will be more than sufficient. You can get it at Radio Shack if you have to.
(Wire FAQ)
Gauge is diameter of the bare wire, no insulation. The higher the number, the smaller the diameter. So 10 gauge wire is ALOT bigger than 22 gauge wire.
MTW wire stands for "Machine Tooling Wire". Usually a PVC insulation with a hard clear coating. Gasoline resistant, sunlight resistant, water resistant, and a bitch to strip sometimes.
Regular PVC insulated wire is great for electrical stuff, but not for around oils or gasoline. It will harden over time, and the insulation will crack.
For electrical things, you want a multistrand wire. Multi strand wire can bend alot without problems. Solid core wire will break if you bend it alot. Solid core is just that. Instead of many copper wires in a bundle, solid core is just one big solid wire. It is normally used to wire houses and is called Romex cable. Its good for houses, bad for anything else.