If the wiring from the ammeter to the starter battery cable connection is doubled up, it might be for extra current carrying capacity. For instance, two 12 ga. wires will carry more total current than a single 10 ga. wire. The ammeter wiring should be able to carry the total generator output, maybe 35 amps or slightly more, to recharge a seriously low battery. Whatever current draw there is from ignition, lights, wipers, heater blower, etc. will be deducted from the amount available for battery charging. In a cold-start situation with nothing but ignition operating, the rest of the generator (or alternator) current will be applied to recharging the battery after the heavy current draw of the starter. Bigger is always better where charging system conductors are concerned. There's no such thing as having too big a wire between the generator and the battery.
Jerry
