Using a generic diagram, you can see the battery at the top, the Big red wire goes to the solonoid to provide power for the starter. A small red wire goes to a fuse, then the amp meter. From the amp meter to the (B) terminal on the key switch. When the switch in in the "run" position the (B) terminal is connected to the (A1) terminal. Follow the red wire from the A1 terminal and you see it connected to the regulator. So when the engine is running the regulator is putting out charge current that goes to the A1 terminal which is connected to the B terminal, through the amp meter, then the fuse and fillaly arrives at the + side of the battery.