[jebx]

well as a set of magnets rotate inside a bunch of copper wires it generates ac current. Things called Rectifiers take that alternating current and turn it into the direct ,or DC currrent , that your truck runs and recharges on. You have at least one "turn-on" wire that comes off the dash light for charging. It has a 12 ignition feed on it and if the alt goes out then it'll get a ground so then the dash light will come on

As a side note, there are single wire aftermarket "self exciting" alternators too.