Ammeter will read zero when the ignition is off of course, when on should show deflection to negative and if you can't see anything switch on the headlights and you should see a much bigger deflection. If nothing then ammeter is not working, so see if it's a mechanical problem with the gauge or connections. I looks okay get out your multimeter and see if the gauge is working electrically. I guess you might have to take the gauge out of the dash to access the connections.If nothing with your tests, then you need a new ammeter or get yours repaired by one of the several companies found on the internet. It seems like ammeters are the first gauges to go in an old car( well for an almost hundred year old car). I think ammeters fell out of favor in dashboards(along with a lot of other gauges), because you do have all the "juice" of the car running through them. Some people favored voltmeters for this reason.