Your 48 could be a positive ground system. Don't know if you converted to alternator and etc.
The terminals on the ammeter are not grounded. So no, don't do that. It may have a "negative symbol" (-) but it's not ground.
You may actually have a volt gauge which does have a terminal to ground.
The wiring of an ammeter does not change when converting to 12V. Unless it was wrong to begin with.
"The current owner"?????? Is that not you? Do you mean previous owner?...and let's don't use the word "current" while we are discussing this
