OK, now we're on the same page! Most older ammeters have a "shunt" built in, which carries most of the current, bypassing the meter movement, which only needs a few miilliamps to function. Simply tapping all the wires onto one terminal, or eliminating the meter and replacing it with a voltmeter isn't a problem. If you're going to an aftermarket ammeter, you'll need to follow the manufacturer's wiring diagram to make it indicate properly.
As long as your voltmeter (if you're using one in place of an ammeter) is connected to a source of straight battery voltage, such as the "ignition" or "accessory" terminal of the ignition switch, it should read battery voltage anytime the switch is on. Connect the other voltmeter lead (usually the "-" terminal) to a good ground, and you're in business!
Jerry
