How a shunt works: Parallel circuit, same Volts, and, different current. The "Ammeter" is one circuit, and the "accessories" are another. Ammeter, reads current to the battery. Everything else is considered an accessory. Please fuse as required.
Excitation: As much as I like Tommy's metaphor(accurate as it is), excitation refers to the field coils magnetic interaction with the armature coils(magnetic field induces current in the armature). For a "self exciting" alternator, some current in the field coils at startup. Instant on alternator. Our beloved, generators did this with permanent magnets at the field coil, and added current(from the regulator) as required for more load. The regulator inside the alternator works much the same way. Modern cars/trucks, use a lot more electrical energy than our old stuff. Power steering, is now electric boosted. A.C. is standard and sound systems are included. Cigar lighter has been replaced by the USB, charging port and maps(a no load item that used to be free) are now a GPS. Add an electric fuel pump, windows, and, heated seats .....you get the picture.
