Factory ammeter

Generally the highest amperage draw on stock electric system is a discharged battery.
That's something an ammeter will show and a voltmeter will not.
Anything close to 40 amps into the battery is going to heat all standard connections. Of all the connectors from the alternator output to the battery, the Packard type push terminals are the weakest. When in the bulkhead there is less ability than other places for the heat to disapate.
The most straightforward solutions are the ones that copy some version of the factory optional wiring. (like shown above, or on this defrost grid equiped car)
edit: That's not to suggest that its good to charge a battery at 40 amps or more. Just that parallel wiring and/or not putting the entire load through the typical standard bulkhead connector will reduce problems with the circuit.