As originally designed, all vehicle loads are connected to splice 1 in the dash harness, on the alternator side of the ammeter, with all power supplied by the alternator while the ignition is on-engine running. The ammeter should only register battery charge/discharge current (that’s it’s purpose). With a fully charged battery in good health, this charge current should be very little, not enough to generate noticeable heat at the ammeter connections. The factory molded ammeter ring terminals screwed together should handle quite a bit of current without any perceived heat under normal circumstances. If the ring terminals have been replaced with aftermarket connections, likely some poor crimping is involved.
Things that commonly alter the original design and can over stress the ammeter and ammeter/bulkhead chare circuit connections on these ammeter equipped older cars include improperly adding aftermarket loads to the battery side of the ammeter (battery/starter relay terminals). In this case, while in operation, the alternator is the source of power, not the battery as some seem to believe, and all this added current load is pulled across the ammeter and all related connections/conductors. Likewise, a failing alternator, or one undersized for the application, will allow vehicle loads to be pulled from the battery while in operation, again placing the ammeter and charge circuit outside of its original design limitations.