OK, I'm answering original poster. Getting confusing with several questioners. The Alt you have can be wired as one wire type by connecting to the spade terminals made for the connector and to the Big Pos lead. You need to read up on this, It really needs a sensing wire/bulb.
If your wiring is a rats nest or mostly in bad/old shape... rewire all. It's fun. I have done vendor kits and made my own. The make my own was same price as a cheap, no extras, low quantity circuit kit. Did it to get experience. I used Packard connectors and contacts and all good components. Old trucks have very little wiring and simple circuits. If your wiring is mostly good and a little bad, just buy wire and some crimped on components to spruce it up. Your wiring size and ammeter questions have been answered very nicely by others.
