Mine is a 59, 3200 originally a 235 converted to a 350. My alternator is the basic 10SI capable of about 55-60 amps max. I don't know the spec capacity of the stock ammeter, but mine has functioned well without any 'shunt' for the 6 years or so and thousands of miles that I have been driving it. If the battery is slightly discharged the meter pegs at first when I start the truck, I just let it idle a few seconds until the meter starts to drop back as the battery begins to be charged. Others may have had problems using the stock ammeter, this is my experience.
There is definitely a problem with that schematic VDO provided. The fuse box should be connected to the same side of the ammeter as the alternator if you intend it to indicate charging and discharging amps. The only things that might be connected directly to the battery are high current items seldom used like power seats, trailer brakes controller, or horn, not the light switch or fuse box. If you really intend to actually read the alternator output in amps (not charging amps) just wire the new ammeter in series into the main power wire coming off the alternator.
Mark
