I have a '48 Willys with 12 volt conversion. It currently has a ammeter gauge that is virtually useless. It always registers the same reading, even when the starter was shorted out or the battery was dying and wouldn't hold a charge. When I turn on the lights or any other electrical system, it very briefly dips for about 1/4 second then returns to 'normal' or 'good". I don't understand why these vehicles use an ammeter instead of a battery volt meter. After all, it is the charge in the battery that i am most interested in monitoring. I don't see any replacement volt meters listed on the catalog. Can anyone explain to me why we use ammeters instead of a 12 volt voltmeter?????