Hi Hanno,
Here is a revised wiring diagram showing the differences in red between a Battery indicator gauge equipped instrument cluster and an ammeter equipped one.
Not a lot required to change over to an ammeter from what I can see. Mainly the routing of the supply from the solenoid to the Battery terminal on the regulator.
Original Regulator Battery terminal to Ignition switch wire can stay even though Mariano's diagram takes current from the Ammeter to the Ignition switch. Same thing electrically however.
Only one Brass bus strip used, too, from Fuel to Temp gauges. If ammeter to Oil pressure gauges had a bus strip all gauges would be "Hot" all the time. They should be only be energised when Ignition switch is thrown.
Thanks again to Mariano Paz's excellent late war wiring plate photos. Makes it so easy to trace wires compared to the rudimentary Ford Manual schematics.
Fairly happy with it all but always glad for "peer review" as they say. It can be easy to miss things.
Cheers,