Ammeter works when key is off?

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