The main reason that voltmeters have taken the place of ammeters in most cases now days is a liability problem the MFG. would prefer to avoid. While I have never experienced it personally, an ammeter can short out an cause a potential fire. All the current to the car and from the alternator are fed through the ammeter, so however much amperage is in the battery can possibly create a safety issue. A voltmeter on the other hand pulls a reading off a line with no circuit running through it. I have never had an ammeter fail to that degree, and wouldn't want it to. I did have the wiring in an old Morris I bought melt the wiring insulation and then the
oil pressure line. It was an aftermarket adaption, pretty standard type thing at the time, and was wired with too small wiring. I do prefer voltmeters for the reason stated in an earlier post. I think they give a better indication of the system condition.
Oddly enough when I looked at your location, Morristown ,NJ., THAT'S the place that my Morris melted it's wires to the gauge....how weird. Had some great times there.