View Full Version : Ammeter vs. Volt gauge

07-11-2018, 11:18 AM
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?????

07-11-2018, 03:10 PM
An ammeter gives you an instantaneous indication of what your electrical system is doing. A battery voltmeter will give you a long term answer, but battery voltage doesn't change rapidly, especially when the battery has a fair charge on it. An ammeter tells you that you are going to have a problem if you don't do something. A voltmeter agrees that you don't have any juice - but you already suspected that.

In the original '48 6-volt configuration, the ammeter measured the total current the electrical system is supplying to the vehicle (less starter and horn). If the current supplied by the BATT terminal of the voltage regulator is "positive" (battery charging), the ammeter reads upscale. If the BATT terminal of the regulator is not providing current, the battery is discharging and the ammeter will read downscale.

I suspect that someone screwed up the 12-volt conversion. If it uses an alternator, the alternator probably isn't compatible with the ammeter.

Here is a good schematic (vs. wiring diagram) of the CJ2 - probably very close to a '48 Willys. It matched the '48 truck very closely.


07-12-2018, 10:21 AM
Outstanding ! Thank you for the schematic's... I'll look into the alternator. I appreciate your input. dan baldwin