Hrockwell:
Assuming it is an ammeter that your are considering replacing with an after-market voltmeter, it may not be a direct replacement. Ammeters measure current flow and often (not always) are to some degree in-line with current flow. Voltmeters measure a voltage (or potential) drop across a resistance. Many times they are set up to measure from some point in a circuit to ground. Ammeters and voltmeters measures different things, even though those things are related, current and voltage respectively. As a result they are usually wired differently. However, replacing the ammeter with a voltmeter is not a big deal, you may just need to re-wire a little bit depending on your current setup.
