My '63 +4 has a ammeter as well as a voltmeter. Not sure what the ammeter does except scare the hell out of Me. As I have an Alternator I pay attention to the Voltmeter and not the ammeter. My Son In Law (auto electric mechanic) says the ammeter is "TROUBLE". Remove it!!!!!!
Having both gives you the fullest picture on battery charging and electrical consumption but OTT on a car. Basically ammeter gives instantaneous info whilst voltmeter gives trend (cause and effect). Your SIL is right though in suggesting you remove ammeter unless it's kept for originality. The shunt within is necessarily a very low resistance so mechanically robust, but the extra cabling and connection's on what is the main power feed to all but starter add a degree of unecessary unreliability.
