Ammeter works when key is off?

Craig Burriss said
Ive been fighting the wiring in my 70 Duster for a while now and I think I’ve almost got it figured out. But one thing that scares me is the factory ammeter works when the key is set to the off position. Like when I turn the headlights on while the ign is off, the ammeter needle drops. I don’t want to kill my battery.
Is this normal or do I have something hooked up wrong. I already have a bunch of wiring diagrams but those aren’t helping me here.
Thanks

Its normal, but I think you'll feel much better knowing why.

The ammeter is in the power feed from the battery.
There is another power feed that carries the alternator's output.
These two feeds join at a welded splice where power is distributed.

So a schematic for power supply and distribution looks like this.

Looking at the schematic, notice the wires that are connected to the battery's positive terminal.
All of those are at battery voltage unless interupted at a switch.

When a switch is closed, a circuit to ground is completed and the current will flow through the ammeter.

When the engine is running, the alternator produces power at a higher voltage than the battery. Therefore power flows from the alternator and does not show on the ammeter, except for what is needed to recharge the battery.