[Tom Endy]

I am of the opinion that an ammeter is an essential device that should be on all cars. A glance at it tells a lot about the condition of the electrical circuit.

When you first start the car up the the ammeter should show a heavy charge going to the battery to replace the power pulled out of it by the starter. This tells you that the generator or alternator is working properly. A few miles down the road the needle should return to zero indicating the battery is charged back up an is no longer being charged. This of course if there is a regulator in the circuit.

If you turn the lights on the generator or alternator will pick up the load and the needle should return to zero. If it does not it is telling you the generator or alternator is not working.

On a Model A with an original undamped ammeter it provides a diagnostic tool. The early cars up to November 1929 did not have the ignition circuit in the ammeter circuit. A service bulletin of November 1929, page 390 changed that by moving one wire on the firewall terminal block from one terminal to the other.

The change allowed you see what was going on when you started the car. As you cranked the engine and before it started you will see the ammeter needle swinging back and forth past the zero. This is due to the points opening and closing. This is telling you that the ignition primary circuit is intact and working properly. If the car does not start the problem is elsewhere.

Tom Endy