I doubt that the resistance across that ammeter's terminals has changed since it was new. Ammeters are simple devices - I can't picture what would result in the resistance increasing. If it is a "-60 - 0 - +60" ammeter, the needle wouldn't move very far when installed on an Alfa. So one solution would be to replace it with a "-30 - 0 - +30" gauge, that better displays the level of amperage that you would get in an Alfa.I'm reasonably sure it DOES cause a drop
Also, if your old ammeter had a meaningful voltage drop, that would mean that it had enough resistance so that when current was passing through, it would get HOT. Do you observe or smell smoke/burning when the engine is off but the headlights are on?
The easiest way to disable the ammeter would be to detach the two heavy wires at its back and join them together with a small screw & nut. Of course, insulate that connection very well, since those wires are not fused. You might even do that temporarily to prove to yourself that the voltage drop is the same with and without the ammeter.Would you just take the amp meter off the wiring and have one more non-working old ornament on the dash, or would you try to make it actually useful?
Not knowing exactly what those two red wires are, and where they go, it's hard to say what would happen if you reconnected them. I'm puzzled why there would be two wires between the battery and fusebox. On 105 models, there is typically one wire to the fusebox and a second to the alternator. But I'm no expert on Alfettas; maybe Alfa ran two, redundant wires in parallel.Also, there were two red wires running from the battery straight to the fusebox and these had been disconnected so the amp meter would work correctly. If I took the amp meter out of the equation I could reconnect these and hopefully it wouldn't hurt the performance.
But sure, if those are the factory wires, and one end is still attached to the fusebox, then taking out the ammeter and re-connecting these wires to the battery "+" post should put the wiring back to its original configuration. Just be sure of where these wires go before re-connecting them - since they are not fused, things will get pretty dramatic if you find that they go to ground.