Disconnect one battery cable on any vehicle you have handy, and fabricate a set of jumper leads from the ammeter to the loose cable end, and another circuit to the battery post, so any current flowing to the vehicle must go through the ammeter. DO NOT TRY TO START THE VEHICLE! It's OK to turn the ignition switch to the "accessory" or "ignition on" position. Turn on any accessories you can, such as high beam headlights, wipers, heater blower, cigarette lighter, etc. Depending on how it's connected, the ammeter will indicate either "charge" or "discharge". Reverse the leads at the ammeter, turn on the load again, and see if the needle swings the other way.
Jerry
